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2.2: Linear Equations in One Variable


Learning Objectives

  • Solve equations in one variable algebraically.
  • Solve a rational equation.
  • Find a linear equation.
  • Given the equations of two lines, determine whether their graphs are parallel or perpendicular.
  • Write the equation of a line parallel or perpendicular to a given line.

Caroline is a full-time college student planning a spring break vacation. To earn enough money for the trip, she has taken a part-time job at the local bank that pays ($15.00/hr), and she opened a savings account with an initial deposit of ($400) on January 15. She arranged for direct deposit of her payroll checks. If spring break begins March 20 and the trip will cost approximately ($2,500), how many hours will she have to work to earn enough to pay for her vacation? If she can only work (4) hours per day, how many days per week will she have to work? How many weeks will it take? In this section, we will investigate problems like this and others, which generate graphs like the line in Figure (PageIndex{1}).

Solving Linear Equations in One Variable

A linear equation is an equation of a straight line, written in one variable. The only power of the variable is (1). Linear equations in one variable may take the form (ax +b=0) and are solved using basic algebraic operations. We begin by classifying linear equations in one variable as one of three types: identity, conditional, or inconsistent.

  • An identity equation is true for all values of the variable. Here is an example of an identity equation: [3x=2x+x onumber ] The solution set consists of all values that make the equation true. For this equation, the solution set is all real numbers because any real number substituted for (x) will make the equation true.
  • A conditional equation is true for only some values of the variable. For example, if we are to solve the equation (5x+2=3x−6), we have the following: [egin{align*} 5x+2&=3x-6 2x &=-8 x&=-4 end{align*} ] The solution set consists of one number: ({−4}). It is the only solution and, therefore, we have solved a conditional equation.
  • An inconsistent equation results in a false statement. For example, if we are to solve (5x−15=5(x−4)), we have the following: [egin{align*} 5x−15 &=5x−20 5x−15-5x &= 5x−20-5x −15 & eq −20 end{align*}]Indeed, (−15≠−20). There is no solution because this is an inconsistent equation.

Solving linear equations in one variable involves the fundamental properties of equality and basic algebraic operations. A brief review of those operations follows.

LINEAR EQUATION IN ONE VARIABLE

A linear equation in one variable can be written in the form

[ax+b=0]

where a and b are real numbers, (a≠0).

Howto: Given a linear equation in one variable, use algebra to solve it

The following steps are used to manipulate an equation and isolate the unknown variable, so that the last line reads (x=)_________, if (x) is the unknown. There is no set order, as the steps used depend on what is given:

  1. We may add, subtract, multiply, or divide an equation by a number or an expression as long as we do the same thing to both sides of the equal sign. Note that we cannot divide by zero.
  2. Apply the distributive property as needed: (a(b+c)=ab+ac).
  3. Isolate the variable on one side of the equation.
  4. When the variable is multiplied by a coefficient in the final stage, multiply both sides of the equation by the reciprocal of the coefficient.

Example (PageIndex{1}): Solving an Equation in One Variable

Solve the following equation: (2x+7=19).

Solution

This equation can be written in the form (ax +b=0) by subtracting 19 from both sides. However, we may proceed to solve the equation in its original form by performing algebraic operations.

[egin{align*} 2x+7&=19 2x&=12qquad ext{Subtract 7 from both sides} x&=6qquad ext{Multiply both sides by } dfrac{1}{2} ext{ or divide by } 2 end{align*}]

The solution is (6).

Exercise (PageIndex{1})

Solve the linear equation in one variable: (2x+1=−9).

Answer

(x=−5)

Example (PageIndex{2}): Solving When the Variable Appears on Both Sides

Solve the following equation: (4(x−3)+12=15−5(x+6)).

Solution

Apply standard algebraic properties.

[egin{align*} 4(x-3)+12&=15-5(x+6) 4x-12+12&=15-5x-30qquad ext{Apply the distributive property} 4x&=-15-5xqquad ext{Combine like terms} 9x&=-15qquad ext{Place x terms on one side and simplify} x&=-dfrac{15}{9}qquad ext{Multiply both sides by } dfrac{1}{9} ext { , the reciprocal of } 9 x&=-dfrac{3}{5} end{align*}]

Analysis

This problem requires the distributive property to be applied twice, and then the properties of algebra are used to reach the final line, (x=-dfrac{3}{5}).

Exercise (PageIndex{2})

Solve the equation in one variable: (−2(3x−1)+x=14−x).

Answer

(x=-3)

Solving a Rational Equation

In this section, we look at rational equations that, after some manipulation, result in a linear equation. If an equation contains at least one rational expression, it is a considered a rational equation. Recall that a rational number is the ratio of two numbers, such as (dfrac{2}{3}) or (dfrac{7}{2}). A rational expression is the ratio, or quotient, of two polynomials. Here are three examples.

[dfrac{x+1}{x^2-4} onumber ]

[dfrac{1}{x-3} onumber ]

or

[dfrac{4}{x^2+x-2} onumber ]

Rational equations have a variable in the denominator in at least one of the terms. Our goal is to perform algebraic operations so that the variables appear in the numerator. In fact, we will eliminate all denominators by multiplying both sides of the equation by the least common denominator (LCD). Finding the LCD is identifying an expression that contains the highest power of all of the factors in all of the denominators. We do this because when the equation is multiplied by the LCD, the common factors in the LCD and in each denominator will equal one and will cancel out.

Example (PageIndex{3}): Solving a Rational Equation

Solve the rational equation:

[dfrac{7}{2x}-dfrac{5}{3x}=dfrac{22}{3} onumber ]

Solution

We have three denominators; (2x),(3x), and (3). The LCD must contain (2x),(3x), and (3). An LCD of (6x) contains all three denominators. In other words, each denominator can be divided evenly into the LCD. Next, multiply both sides of the equation by the LCD (6x).

[egin{align*}
(6x)left[dfrac{7}{2x}-dfrac{5}{3x} ight]&=left[dfrac{22}{3} ight](6x)
(6x)left(dfrac{7}{2x} ight)-(6x)left(dfrac{5}{3x} ight)&=left(dfrac{22}{3} ight)(6x)qquad ext{Use the distributive property. Cancel out the common factors}
3(7)-2(5)&=22(2x)qquad ext{Multiply remaining factors by each numerator.}
21-10&=44x
11&=44x
dfrac{11}{44}&=x
dfrac{1}{4}&=x
end{align*}]

A common mistake made when solving rational equations involves finding the LCD when one of the denominators is a binomial—two terms added or subtracted—such as ((x+1)). Always consider a binomial as an individual factor—the terms cannot be separated. For example, suppose a problem has three terms and the denominators are (x), (x−1), and (3x−3). First, factor all denominators. We then have (x), ((x−1)), and (3(x−1)) as the denominators. (Note the parentheses placed around the second denominator.) Only the last two denominators have a common factor of ((x−1)). The x in the first denominator is separate from the (x) in the ((x−1)) denominators. An effective way to remember this is to write factored and binomial denominators in parentheses, and consider each parentheses as a separate unit or a separate factor. The LCD in this instance is found by multiplying together the (x), one factor of ((x−1)), and the 3. Thus, the LCD is the following:

(x(x−1)3=3x(x−1))

So, both sides of the equation would be multiplied by (3x(x−1)). Leave the LCD in factored form, as this makes it easier to see how each denominator in the problem cancels out.

Another example is a problem with two denominators, such as (x) and (x^2+2x). Once the second denominator is factored as (x^2+2x=x(x+2)), there is a common factor of (x) in both denominators and the LCD is (x(x+2)).

Sometimes we have a rational equation in the form of a proportion; that is, when one fraction equals another fraction and there are no other terms in the equation.

[dfrac{a}{b}=dfrac{c}{d}]

We can use another method of solving the equation without finding the LCD: cross-multiplication. We multiply terms by crossing over the equal sign.

Multiply a(d) and b(c), which results in (ad=bc).

Any solution that makes a denominator in the original expression equal zero must be excluded from the possibilities.

RATIONAL EQUATIONS

A rational equation contains at least one rational expression where the variable appears in at least one of the denominators.

Howto: Given a rational equation, solve it.

  1. Factor all denominators in the equation.
  2. Find and exclude values that set each denominator equal to zero.
  3. Find the LCD.
  4. Multiply the whole equation by the LCD. If the LCD is correct, there will be no denominators left.
  5. Solve the remaining equation.
  6. Make sure to check solutions back in the original equations to avoid a solution producing zero in a denominator

Example (PageIndex{4}): Solving a Rational Equation without Factoring

Solve the following rational equation:

(dfrac{2}{x}-dfrac{3}{2}=dfrac{7}{2x})

Solution

We have three denominators: (x), (2), and (2x). No factoring is required. The product of the first two denominators is equal to the third denominator, so, the LCD is (2x). Only one value is excluded from a solution set, (0). Next, multiply the whole equation (both sides of the equal sign) by (2x).

The proposed solution is (−1), which is not an excluded value, so the solution set contains one number, (x=−1), or ({−1}) written in set notation.

Exercise (PageIndex{4})

Solve the rational equation:

(dfrac{2}{3x}=dfrac{1}{4}-dfrac{1}{6x})

Answer

(x=dfrac{10}{3})

Example (PageIndex{5}): Solving a Rational Equation by Factoring the Denominator

Solve the following rational equation:

(dfrac{1}{x}=dfrac{1}{10}-dfrac{3}{4x})

Solution

First find the common denominator. The three denominators in factored form are (x,10=2⋅5), and (4x=2⋅2⋅x). The smallest expression that is divisible by each one of the denominators is (20x). Only (x=0) is an excluded value. Multiply the whole equation by (20x).

[egin{align*} 20xleft(dfrac{1}{x} ight)&= left(dfrac{1}{10}-dfrac{3}{4x} ight)20x 20&= 2x-15 35&= 2x dfrac{35}{2}&= x end{align*}]

The solution is (dfrac{35}{2}).

Exercise (PageIndex{5})

Solve the rational equation:

[-dfrac{5}{2x}+dfrac{3}{4x}=-dfrac{7}{4} onumber ]

Answer

(x=1)

Example (PageIndex{6}): Solving Rational Equations with a Binomial in the Denominator

Solve the following rational equations and state the excluded values:

  1. (dfrac{3}{x-6}=dfrac{5}{x})
  2. (dfrac{x}{x-3}=dfrac{5}{x-3}-dfrac{1}{2})
  3. (dfrac{x}{x-2}=dfrac{5}{x-2}-dfrac{1}{2})

Solution

a.

The denominators (x) and (x−6) have nothing in common. Therefore, the LCD is the product (x(x−6)). However, for this problem, we can cross-multiply.

[egin{align*} dfrac{3}{x-6}&=dfrac{5}{x} 3x&=5(x-6)qquad ext{Distribute.} 3x&=5x-30 -2x&=-30 x&=15 end{align*}]

The solution is (15). The excluded values are (6) and (0).

b.

The LCD is (2(x−3)). Multiply both sides of the equation by (2(x−3)).

[egin{align*} 2(x-3)left [dfrac{x}{x-3} ight ]&= left [dfrac{5}{x-3}-dfrac{1}{2} ight ]2(x-3) dfrac{2(x-3)x}{x-3}&= dfrac{2(x-3)5}{x-3}-dfrac{2(x-3)}{2} 2x&= 10-(x-3) 2x&= 13-x 3x&= 13 x&= dfrac{13}{3} end{align*}]

The solution is (dfrac{13}{3}). The excluded value is (3).

c.

The least common denominator is (2(x−2)). Multiply both sides of the equation by (x(x−2)).

[egin{align*} 2(x-2)left [dfrac{x}{x-2} ight ]&= left [dfrac{5}{x-2}-dfrac{1}{2} ight ]2(x-2) 2x&= 10-(x-2) 2x&= 12-x 3x&= 12 x&= 4 end{align*}]

The solution is (4). The excluded value is (2).

Exercise (PageIndex{6})

Solve (dfrac{-3}{2x+1}=dfrac{4}{3x+1}). State the excluded values.

Answer

(x=-dfrac{7}{17}). Excluded values are (x=−12) and (x=−13).

Example (PageIndex{7}): Solving a Rational Equation with Factored Denominators and Stating Excluded Values

Solve the rational equation after factoring the denominators: (dfrac{2}{x+1}-dfrac{1}{x-1}=dfrac{2x}{x^2-1}). State the excluded values.

Solution

We must factor the denominator (x^2−1). We recognize this as the difference of squares, and factor it as ((x−1)(x+1)). Thus, the LCD that contains each denominator is ((x−1)(x+1)). Multiply the whole equation by the LCD, cancel out the denominators, and solve the remaining equation.

[egin{align*} (x+1)(x-1)left [dfrac{2}{x+1}-dfrac{1}{x-1} ight ]&= left [dfrac{2x}{x^2-1} ight ](x+1)(x-1) 2(x-1)-(x+1)&= 2x 2x-2-x-1&= 2x ext{ Distribute the negative sign} -3-x&= 0 x&= -3 end{align*}]

The solution is (−3). The excluded values are (1) and (−1).

Exercise (PageIndex{7})

Solve the rational equation:

(dfrac{2}{x-2}+dfrac{1}{x+1}=dfrac{1}{x^2-x-2})

Answer

(x=dfrac{1}{3})

Finding a Linear Equation

Perhaps the most familiar form of a linear equation is the slope-intercept form, written as [y=mx+b] where (m= ext{slope}) and (b= ext{y−intercept.}) Let us begin with the slope.

The slope of a line refers to the ratio of the vertical change in (y) over the horizontal change in (x) between any two points on a line. It indicates the direction in which a line slants as well as its steepness. Slope is sometimes described as rise over run.

[m=dfrac{y_2-y_1}{x_2-x_1}]

If the slope is positive, the line slants to the right. If the slope is negative, the line slants to the left. As the slope increases, the line becomes steeper. Some examples are shown in Figure (PageIndex{2}). The lines indicate the following slopes: (m=−3), (m=2), and (m=dfrac{1}{3}).

THE SLOPE OF A LINE

The slope of a line, (m), represents the change in (y) over the change in (x). Given two points, ((x_1,y_1)) and ((x_2,y_2)), the following formula determines the slope of a line containing these points:

[m=dfrac{y_2-y_1}{x_2-x_1}]

Example (PageIndex{8}): Finding the Slope of a Line Given Two Points

Find the slope of a line that passes through the points ((2,−1)) and ((−5,3)).

Solution

We substitute the (y)-values and the (x)-values into the formula.

[egin{align*} m&= dfrac{3-(-1)}{-5-2} &= dfrac{4}{-7} &= -dfrac{4}{7} end{align*}]

The slope is (-dfrac{4}{7})

Analysis

It does not matter which point is called ((x_1,y_1)) or ((x_2,y_2)). As long as we are consistent with the order of the (y) terms and the order of the (x) terms in the numerator and denominator, the calculation will yield the same result.

Exercise (PageIndex{8})

Find the slope of the line that passes through the points ((−2,6)) and ((1,4)).

Answer

(m=-dfrac{2}{3})

Example (PageIndex{9}): Identifying the Slope and y-intercept of a Line Given an Equation

Identify the slope and (y)-intercept, given the equation (y=-dfrac{3}{4}x-4).

Solution

As the line is in (y=mx+b) form, the given line has a slope of (m=-dfrac{3}{4}). The (y)-intercept is (b=−4).

Analysis

The (y)-intercept is the point at which the line crosses the (y)-axis. On the (y)-axis, (x=0). We can always identify the (y)-intercept when the line is in slope-intercept form, as it will always equal (b). Or, just substitute (x=0) and solve for (y).

The Point-Slope Formula

Given the slope and one point on a line, we can find the equation of the line using the point-slope formula.

[y−y_1=m(x−x_1)]

This is an important formula, as it will be used in other areas of college algebra and often in calculus to find the equation of a tangent line. We need only one point and the slope of the line to use the formula. After substituting the slope and the coordinates of one point into the formula, we simplify it and write it in slope-intercept form.

THE POINT-SLOPE FORMULA

Given one point and the slope, the point-slope formula will lead to the equation of a line:

[y−y_1=m(x−x_1)]

Example (PageIndex{10}): Finding the Equation of a Line Given the Slope and One Point

Write the equation of the line with slope (m=−3) and passing through the point ((4,8)). Write the final equation in slope-intercept form.

Solution

Using the point-slope formula, substitute (−3) for m and the point ((4,8)) for ((x_1,y_1)).

[egin{align*} y-y_1&= m(x-x_1) y-8&= -3(x-4) y-8&= -3x+12 y&= -3x+20 end{align*}]

Analysis

Note that any point on the line can be used to find the equation. If done correctly, the same final equation will be obtained.

Exercise (PageIndex{10})

Given (m=4), find the equation of the line in slope-intercept form passing through the point ((2,5)).

Answer

(y=4x−3)

Example (PageIndex{11}): Finding the Equation of a Line Passing Through Two Given Points

Find the equation of the line passing through the points ((3,4)) and ((0,−3)). Write the final equation in slope-intercept form.

Solution

First, we calculate the slope using the slope formula and two points.

[egin{align*} m&= dfrac{-3-4}{0-3} m&= dfrac{-7}{-3} m&= dfrac{7}{3} end{align*}]

Next, we use the point-slope formula with the slope of (dfrac{7}{3}), and either point. Let’s pick the point ((3,4)) for ((x_1,y_1)).

[egin{align*} y-4&= dfrac{7}{3}(x-3) y-4&= dfrac{7}{3}x-7 y&= dfrac{7}{3}-3 end{align*}]

In slope-intercept form, the equation is written as (y=dfrac{7}{3}-3)

Analysis

To prove that either point can be used, let us use the second point ((0,−3)) and see if we get the same equation.

[egin{align*} y-(-3)&= dfrac{7}{3}(x-0) y+3&= dfrac{7}{3}x y&= dfrac{7}{3}-3 end{align*}]

We see that the same line will be obtained using either point. This makes sense because we used both points to calculate the slope.

Standard Form of a Line

Another way that we can represent the equation of a line is in standard form. Standard form is given as

[Ax+By=C]

where (A), (B), and (C) are integers. The (x)- and (y)-terms are on one side of the equal sign and the constant term is on the other side.

Example (PageIndex{12}): Finding the Equation of a Line and Writing It in Standard Form

Find the equation of the line with (m=−6) and passing through the point (left(dfrac{1}{4},−2 ight)). Write the equation in standard form.

Solution

We begin using the point-slope formula.

[egin{align*} y-(-2)&= -6left(x-dfrac{1}{4} ight) y+2&= -6x+dfrac{3}{2} end{align*}]

From here, we multiply through by (2), as no fractions are permitted in standard form, and then move both variables to the left aside of the equal sign and move the constants to the right.

[egin{align*} 2(y+2)&= left(-6x+dfrac{3}{2} ight)2 2y+4&= -12x+3 12x+2y&= -1 end{align*}]

This equation is now written in standard form.

Exercise (PageIndex{12})

Find the equation of the line in standard form with slope (m=−dfrac{1}{3}) and passing through the point ((1,13)).

Answer

(x+3y=2)

Vertical and Horizontal Lines

The equations of vertical and horizontal lines do not require any of the preceding formulas, although we can use the formulas to prove that the equations are correct. The equation of a vertical line is given as

[x=c]

where (c) is a constant. The slope of a vertical line is undefined, and regardless of the (y)-value of any point on the line, the (x)-coordinate of the point will be (c).

Suppose that we want to find the equation of a line containing the following points: ((−3,−5)),((−3,1)),((−3,3)), and ((−3,5)). First, we will find the slope.

(m=dfrac{5-3}{-3-(-3)}=dfrac{2}{0})

Zero in the denominator means that the slope is undefined and, therefore, we cannot use the point-slope formula. However, we can plot the points. Notice that all of the (x)-coordinates are the same and we find a vertical line through (x=−3). See Figure (PageIndex{3}).

The equation of a horizontal line is given as

[y=c]

where (c) is a constant. The slope of a horizontal line is zero, and for any (x)-value of a point on the line, the (y)-coordinate will be (c).

Suppose we want to find the equation of a line that contains the following set of points: ((−2,−2)),((0,−2)),((3,−2)), and ((5,−2)). We can use the point-slope formula. First, we find the slope using any two points on the line.

[egin{align*} m&= dfrac{-2-(-2)}{0-(-2)} &= dfrac{0}{2} &= 0 end{align*}]

Use any point for ((x_1,y_1)) in the formula, or use the y-intercept.

[egin{align*} y-(-2)&= 0(x-3) y+2&= 0 y&= -2 end{align*}]

The graph is a horizontal line through (y=−2). Notice that all of the y-coordinates are the same. See Figure (PageIndex{3}).

Example (PageIndex{13}): Finding the Equation of a Line Passing Through the Given Points

Find the equation of the line passing through the given points: ((1,−3)) and ((1,4)).

Solution

The (x)-coordinate of both points is (1). Therefore, we have a vertical line, (x=1).

Exercise (PageIndex{13})

Find the equation of the line passing through ((−5,2)) and ((2,2)).

Answer

Horizontal line: (y=2)

Determining Whether Graphs of Lines are Parallel or Perpendicular

Parallel lines have the same slope and different y-intercepts. Lines that are parallel to each other will never intersect. For example, Figure (PageIndex{4}) shows the graphs of various lines with the same slope, (m=2).

All of the lines shown in the graph are parallel because they have the same slope and different y-intercepts.

Lines that are perpendicular intersect to form a (90^{circ}) -angle. The slope of one line is the negative reciprocal of the other. We can show that two lines are perpendicular if the product of the two slopes is (−1:m_1⋅m_2=−1). For example, Figure (PageIndex{5}) shows the graph of two perpendicular lines. One line has a slope of (3); the other line has a slope of (-dfrac{1}{3}).

[egin{align*} m_1cdot m_2&= -1 3cdot left (-dfrac{1}{3} ight )&= -1 end{align*}]

Example (PageIndex{14}): Graphing Two Equations, and Determining Whether the Lines are Parallel, Perpendicular, or Neither

Graph the equations of the given lines, and state whether they are parallel, perpendicular, or neither: (3y=−4x+3) and (3x−4y=8).

Solution

The first thing we want to do is rewrite the equations so that both equations are in slope-intercept form.

First equation:

[egin{align*} 3y&= -4x+3 y&= -dfrac{4}{3}x+1 end{align*}]

Second equation:

[egin{align*} 3x-4y&= 8 -4y&= -3x+8 y&= dfrac{3}{4}x-2 end{align*}]

See the graph of both lines in Figure (PageIndex{6}).

From the graph, we can see that the lines appear perpendicular, but we must compare the slopes.

[egin{align*} m_1&=-dfrac{4}{3} m_2&=dfrac{3}{4} m_1cdot m_2&=left(-dfrac{4}{3} ight)left(dfrac{3}{4} ight) &=-1 end{align*}]

The slopes are negative reciprocals of each other, confirming that the lines are perpendicular.

Exercise (PageIndex{14})

Graph the two lines and determine whether they are parallel, perpendicular, or neither: (2y−x=10) and (2y=x+4).

Answer

Parallel lines: equations are written in slope-intercept form.

Writing the Equations of Lines Parallel or Perpendicular to a Given Line

As we have learned, determining whether two lines are parallel or perpendicular is a matter of finding the slopes. To write the equation of a line parallel or perpendicular to another line, we follow the same principles as we do for finding the equation of any line. After finding the slope, use the point-slope formula to write the equation of the new line.

Given an equation for a line, write the equation of a line parallel or perpendicular to it.

  1. Find the slope of the given line. The easiest way to do this is to write the equation in slope-intercept form.
  2. Use the slope and the given point with the point-slope formula.
  3. Simplify the line to slope-intercept form and compare the equation to the given line.

Example (PageIndex{15}): Writing the Equation of a Line Parallel to a Given Line Passing Through a Given Point

Write the equation of line parallel to a (5x+3y=1) and passing through the point ((3,5)).

Solution

First, we will write the equation in slope-intercept form to find the slope.

[egin{align*} 5x+3y&= 1 3y&= -5x+1 y&= -dfrac{5}{3}+dfrac{1}{3} end{align*}]

The slope is (m=−dfrac{5}{3}). The y-intercept is (13), but that really does not enter into our problem, as the only thing we need for two lines to be parallel is the same slope. The one exception is that if the (y)-intercepts are the same, then the two lines are the same line. The next step is to use this slope and the given point with the point-slope formula.

[egin{align*} y-5&= -dfrac{5}{3}(x-3) y-5&= -dfrac{5}{3}x+5 y&= -dfrac{5}{3}+10 end{align*}]

The equation of the line is (y=−dfrac{5}{3}x+10). See Figure (PageIndex{8}).

Exercise (PageIndex{15})

Find the equation of the line parallel to (5x=7+y) and passing through the point ((−1,−2)).

Answer

(y=5x+3)

Example (PageIndex{16}): Finding the Equation of a Line Perpendicular to a Given Line Passing Through a Given Point

Find the equation of the line perpendicular to (5x−3y+4=0space(−4,1)).

Solution

The first step is to write the equation in slope-intercept form.

[egin{align*} 5x-3y+4&= 0 -3y&= -5x-4 y&= dfrac{5}{3}x+dfrac{4}{3} end{align*}]

We see that the slope is (m=dfrac{5}{3}). This means that the slope of the line perpendicular to the given line is the negative reciprocal, or (-dfrac{3}{5}). Next, we use the point-slope formula with this new slope and the given point.

[egin{align*} y-1&= -dfrac{3}{5}(x-(-4)) y-1&= -dfrac{3}{5}x-dfrac{12}{5} y&= -dfrac{3}{5}x-dfrac{12}{5}+dfrac{5}{5} y&= -dfrac{3}{5}-dfrac{7}{5} end{align*}]

Media

Access these online resources for additional instruction and practice with linear equations.

  1. Solving rational equations
  2. Equation of a line given two points
  3. Finding the equation of a line perpendicular to another line through a given point
  4. Finding the equation of a line parallel to another line through a given point

Key Concepts

  • We can solve linear equations in one variable in the form (ax +b=0) using standard algebraic properties. See Example and Example.
  • A rational expression is a quotient of two polynomials. We use the LCD to clear the fractions from an equation. See Example and Example.
  • All solutions to a rational equation should be verified within the original equation to avoid an undefined term, or zero in the denominator. See Example and Example.
  • Given two points, we can find the slope of a line using the slope formula. See Example.
  • We can identify the slope and (y)-intercept of an equation in slope-intercept form. See Example.
  • We can find the equation of a line given the slope and a point. See Example.
  • We can also find the equation of a line given two points. Find the slope and use the point-slope formula. See Example.
  • The standard form of a line has no fractions. See Example.
  • Horizontal lines have a slope of zero and are defined as (y=c), where (c) is a constant.
  • Vertical lines have an undefined slope (zero in the denominator), and are defined as (x=c), where (c) is a constant. See Example.
  • Parallel lines have the same slope and different (y)-intercepts. See Example.
  • Perpendicular lines have slopes that are negative reciprocals of each other unless one is horizontal and the other is vertical. See Example.

Excercise 2.2 Linear Equations in One Variable- NCERT Solutions Class 8

If you subtract (eginfrac<1><2>end) from a number and multiply the result by (eginfrac<1><2>end) , you get (eginfrac<1><8>end) . What is the number?

Solution

Video Solution

Forming a linear equation for the given problem statement and solving it will lead to the solution.

What is known?

(i) (eginfrac<1><2>end) is subtracted from a number.

(ii) Result is multiplied by (eginfrac<1><2>end)

What is unknown?

(i) (eginfrac<1><2>end) is subtracted from a number (egin o x - frac<1><2>end)

(ii) Result is multiplied by (eginfrac<1> <2> o frac<1><2>(x - frac<1><2>)end)


1. If you subtract ½ from a number and multiply the result by ½, you get ⅛ . What is the number?
Solution:
Let the number be x.
According to question,
( x – ½ ) × ½ = ⅛
x/2 – ¼ = ⅛
x/2 = ⅛ + ¼
x/2 = ⅜
x = ⅜×2
x = ¾

2. The perimeter of a rectangular swimming pool is 154 m. Its length is 2 m more than twice its breadth. What are the length and the breadth of the pool?
Solution:
Perimeter of a rectangular swimming pool = 154 m.
Let the breadth of rectangle = x
According to question,
Length of rectangle = 2x + 2
Perimeter of rectangle
= 2( Length + breadth)
= 2( 2x +2 + x)
= 154
2( 2x +2 + x) = 154
2(3x + 2) = 154
6x + 4 = 154
6x = 154 -4
6x = 150
x = 150/6
x = 25
Therefore, Breadth = 25m.
Length = 2×25 + 2 = 52m.

3. The base of an isosceles triangle is 4/3 cm. The perimeter of the triangle is 4_2/15cm.
What is the length of either of the remaining equal sides?
Solution:
Base of isosceles triangle = 4/3
Perimeter of triangle = 4_2/15 cm = 62/15cm
Let the length of equal sides of triangle be x.
According to the question,
4/3 + x + x = 62/15
2x = 62/15 – 4/3
2x = (62- 20 )/15
2x = 42/15
x = 62/15 × ½
x = 42/30 cm
x = 7/5 cm
The length of either of the remaining equal sides aer 7/5 cm.

4. Sum of two numbers is 95. If one exceeds the other by 15, find the numbers.
Solution:
Let one of the numbers be = x.
Then, the other number becomes x + 15. According to the question,
x + x + 15 = 95
2x = 95 – 15
2x = 80
x = 80/2
x = 40
First number = x = 40
And, other number = x + 15 = 40 + 15 = 55.

5. Two numbers are in the ratio 5:3. If they differ by 18 , what are the numbers?
Solution:
Let the two numbers be 5x and 3x.
According to the question,
5x – 3x = 18
2x = 18
x = 18/2
x = 9
The numbers are 5x = 5 × 9 = 45
And 3x = 3 × 9 = 27.

6. Three consecutive integers add up to 51. What are these integers?
Solution:
Let the three consecutive integers be x, x + 1, x +2.
According to the question,
x + x + 1 + x + 2 = 51
3x + 3 = 51
3x = 51 – 3
3x = 48
x = 48 /3
x = 16
thus, the integers are
x = 16
x + 1 = 17
x + 2 = 18

7. The sum of three consecutive multiples of 8 is 888. Find the multiples.
Solution:
Let the three consecutive multiples of 8 be 8x, 8( x + 1 ), 8( x + 2 ).
According to the question,
8x + 8(x + 1 ) + 8( x + 2 ) = 888
8( x + x + 1 + x + 2 ) = 888 ( taking 8 as common )
8( 3x + 3 ) = 888
3x + 3 = 888/8
3x + 3 = 111
3x = 111 – 3 = 108
x = 108/3
x = 36
Thus, the three consecutive multiples of 8 are:
8x = 8 × 36 = 288
8( x + 1 ) = 8 × 37 = 296
8( x + 2 ) = 8 × 38 = 304

8. Three consecutive integers are such that when they are taken in increasing order and multiplied by 2,3 and 4 respectively, they add up to 74. Find these.
Solution:
Let the three consecutive integers are x, x + 1, x +2.
According to the question,
2x + 3( x + 1 ) + 4( x + 2 ) = 74
2x + 3x + 3 + 4x + 8 = 74
9x + 11 = 74
9x = 74 – 11
9x = 63
x = 63/9
x = 7
Thus, the numbers are:
x = 7
x + 1 = 8
x + 2 = 9

9. The ages of Rahul and Haroon are in the ratio 5:7. Four years later the sum of their ages will be 56 years. What are their present ages?
Solution:
Let the ages of Rahul and Haroon be 5x and 7x.
According to the question,
5x + 4 + 7x + 4 = 56
12x + 8 = 56
12x = 56 – 8
12x = 48
x = 48/12
x = 4
Therefore,
Present age of Rahul = 5x = 5 × 4 = 20
And, Present age of Haroon = 7x = 7 × 4 = 28

10. The number of boys and girls in a class are the ratio 7:5. The number of boys is 8 more than the number of girls. What is the total class strength?
Solution:
Let the number of boys be 7x and girls be 5x.
According to the question,
7x = 5x +8
7x – 5x = 8
2x = 8
x = 8/4
x = 2
Therefore, Number of boys = 7 × 4 = 28
And, Number of girls = 5 × 4 = 20
Total number of students = 20 + 28 = 48

11. Baichung’s father is 26 years younger than Baichung’s grandfather and 29 years older than Baichung. The sum of the ages of all the three is 135 years. What is the age of each one of them?
Solution:
Let the age of Baichung’s father be x.
Then, the age of Baichung’s grandfather = x + 26.
and, Age of Baichung = x – 29.
According to the question,
x + x + 26 + x – 29 = 135
3x – 3 = 135
3x = 135 + 3
3x = 138/3
x = 46
Age of Baichung’s father = x = 46
Age of Baichung’s grandfather = x +26 = 72
Age of Baichung = x – 29 = 17

12. Fifteen years from now Ravi’s age will be four times his present age. What is Ravi’s present age?
Solution:
Let the present age of Ravi be x.
Fifteen years later, Ravi age will be x + 15years.
According to the question,
x + 15 = 4x
4x – x = 15
3x = 15
x = 15/3
x = 5
Therefore, present age of Ravi = 5 years.

13. A rational number is such that when you multiply it by 5/2 and add 2/3 to the product, you get, -7/12. What is the number?
Solution:
Let the rational number be x.
According to the question,
x × (5/2) + 2/3 = -7/12
5x/2 + 2/3 = -7/12
5x/2 = -7/12 -2/3
5x/2 = ( -7 -8)/12
5x/2 = -15/12
5x/2 = -5/4
x = (-5/4) × (2/5)
x = -10/20
x = -1/2
Therefore, the rational number is -1/2.

14. Lakshmi is a cashier in a bank. She has currency notes of denominations 100, 50 and 10, respectively. The ratio of the number of these notes is 2:3:5. The total cash with Lakshmi is 4,00,000. How many notes of each denomination does she have?
Solution:
Let the numbers to notes of Rs.100, Rs.50, Rs.10, be 2x, 3x, and 5x respectively.
Value of Rs.100 = 2x × 100 = 200x
Value of Rs.50 = 3x × 50 = 150x
Value of Rs.10 = 5x × 10 = 50x.
According to the question,
200x + 150x + 50x = 4,00,000
400x = 4,00,000
x = 4,00,000/400
x = 1000
Numbers of Rs.100 notes = 2x = 2000
Numbers of Rs.50 notes = 3x = 3000
Numbers of Rs.10 notes = 5x = 5000

15. I have a total of Rs.300 in coins of denomination Rs.1, Rs.2 and Rs.5. The number of Rs.2 coins is 3 times the number of Rs.5 coins. The total number of coins is 160. How many coins of each denomination are with me?
Solution:
Let the number of Rs.5 coins be x.
Then,
Number of Rs.2 coins = 3x
Number of Rs.1 coins = 160 – 4x
Now,
Value of Rs.5 coins = x × 5 = 5x
Value of Rs.2 coins = 3x × 2 = 6x
Value of Rs.1 coins = (160 – 4x) × 1 = 160 -4x
According to the question,
5x +6x + 160 – 4x = 300
11x + 160 – 4x = 300
7x = 300 – 160
7x = 140
x = 140/7
x = 20
Number of Rs.5 coins = x = 20
Number of Rs.2 coins = 3x = 60
Number of Rs.1 coins = 160 – 4x = 160 -80
= 80

16. The organisers of an essay competition decide that a winner in the competition gets a prize of Rs.100 and a participant who does not win gets a prize of Rs.25. The total prize money distributed is Rs.3000. Find the number of winners, if the total number of participants is 63.
Solution:
Let the numbers of winner be x.
Then, the number of participants who didn’t win = 63 – x
Total money given to the winner = x × 100 = 100x
Total money given to participant who didn’t win = 25( 63 – x )
According to the question:
100x + 25( 63 – x ) = 3,000
100x + 1575 – 25x = 3,000
75x = 3,000 – 1575
75x = 1425
x = 1425/75
x = 19
Therefore, the number of winners are 19.


Chapter 2 Ex.2.1 Question 3

Solution

Video Solution

What is known?

What is unknown?

In an equation values of left-hand side (LHS) and right-hand side (RHS) are equal. The two sides of the equation are balanced. We perform mathematical operations so that the balance is not disturbed.

Transposing (2) to LHS we get,


NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Ex 2.6

NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Exercise 2.6

Solve the following equations.
Ex 2.6 Class 8 Maths Question 1.
(frac < 8x-3 > < 3x >=2)
Solution:
We have (frac < 8x-3 > < 3x >=2)
⇒ (frac < 8x-3 >< 3x >) = (frac < 2 >< 1 >)
⇒ 8x – 3 = 2 × 3x (Cross-multiplication)
⇒ 8x – 3 = 6x
⇒ 8x – 6x = 3 (Transposing 6x to LHS and 3 to RHS)
⇒ 2x = 3
⇒ x = (frac < 3 >< 2 >)

Ex 2.6 Class 8 Maths Question 2.
(frac < 9x >< 7-6x >) = 15
Solution:
we have (frac < 9x >< 7-6x >) = 15
⇒ (frac < 9x >< 7-6x >) = (frac < 15 >< 1 >)
⇒ 9x = 15(7 – 6x) (Cross-multiplication)
⇒ 9x = 105 – 90x (Solving the bracket)
⇒ 9x + 90x = 105 (Transposing 90x to LHS)
⇒ 99x = 105
⇒ x = (frac < 105 >< 99 >)
⇒ x = (frac < 35 >< 33 >)

Ex 2.6 Class 8 Maths Question 3.
(frac < z > < z+15 >=frac < 4 >< 9 >)
Solution:
We have (frac < z > < z+15 >=frac < 4 >< 9 >)
⇒ 9z = 4 (z + 15) (Cross-multiplication)
⇒ 9z = 4z + 60 (Solving the bracket)
⇒ 9z – 42 = 60
⇒ 5z = 60
⇒ z = 12

Ex 2.6 Class 8 Maths Question 4.
(frac < 3y+4 > < 2-6y >=frac < -2 >< 5 >)
Solution:
we have (frac < 3y+4 > < 2-6y >=frac < -2 >< 5 >)
⇒ 5(3y + 4) = -2(2 – 6y) (Cross-multiplication)
⇒ 15y + 20 = -4 + 12y (Solving the bracket)
⇒ 15y – 12y = -4 – 20 (Transposing 12y to LHS and 20 to RHS)
⇒ 3y = -24 (Transposing 3 to RHS) -24
⇒ y = -8

Ex 2.6 Class 8 Maths Question 5.
(frac < 7y+4 > < y+2 >=frac < -4 >< 3 >)
Solution:
we have (frac < 7y+4 > < y+2 >=frac < -4 >< 3 >)
⇒ 3(7y + 4) = -4 (y + 2) (Corss-multiplication)
⇒ 21y + 12 = -4y – 8 [Solving the bracket]
⇒ 21y + 4y = -12 – 8 [Transposing 4y to LHS and 12 to RHS]
⇒ 25y = -20 [Transposing 25 to RHS]
⇒ y = (frac < -4 >< 5 >)

Ex 2.6 Class 8 Maths Question 6.
The ages of Hari and Harry are in the ratio 5 : 7. Four years from now the ratio of their ages will be 3 : 4. Find their present ages.
Solution:
Let the present ages of Hari and Harry be 5x years and 7x years respectively.
After 4 years Hari’s age will be (5x + 4) years and Harry’s age will be (7x + 4) years.
As per the conditions, we have
(frac < 5x+4 > < 7x+4 >=frac < 3 >< 4 >)
⇒ 4(5x + 4) = 3(7x + 4) (Cross-multiplication)
⇒ 20x + 16 = 21x + 12 (Solving the bracket)
⇒ 20x – 21x = 12 – 16 (Transposing 21x to LHS and 16 to RHS)
⇒ -x = -4
⇒ x = 4
Hence the present ages of Hari and Harry are 5 × 4 = 20years and 7 × 4 = 28years respectively.

Ex 2.6 Class 8 Maths Question 7.
The denominator of a rational number is greater than its numerator by 8. If the numerator is increased by 17 and the denominator is decreased by 1, the number obtained is (frac < 3 >< 2 >). Find the rational number.
Solution:
Let the numerator of the rational number be x.
Denominator = (x + 8)
As per the conditions, we have

⇒ 2(x + 17) = 3(x + 7) (Cross-multiplication)
⇒ 2x + 34 = 3x + 21 (Solving the bracket)
⇒ 2x – 3x = 21 – 34 (Transposing 3x to LHS and 34 to RHS)
⇒ -x = -13
⇒ x = 13
Thus, numerator = 13
and denominator = 13 + 8 = 21
Hence the rational number is (frac < 13 >< 21 >).


Question 1.
If you subtract (frac < 1 > < 2 >) from a number and multiply the result (frac < 1 > < 2 >) by you get (frac < 1 > < 8 >) What is the number ?
Solution.

Question 2.
The perimeter of a rectangular swimming pool is 154 m. Its length is 2 m more than twice its breadth. What are the length and the breadth of the pool?
Solution.

Question 3.
The base of an isosceles triangle is (frac < 4 > < 3 >)cm. The perimeter of the triangle is (4frac < 2 > < 15 >)cm. What is the length of either of the remaining equal sides ?
Solution.

Question 4.
Sum of two numbers is 95. If one exceeds the other by 15, find the numbers.
Solution.

Question 5.
Two numbers are in the ratio 5 :3. If they differ by 18, what are the numbers?
Solution.

Question 6.
Three consecutive integers add up to 51. What are these integers ?
Solution.

Question 7.
The sum of three consecutive multiples of 8 is 888. Find the multiples.
Solution.

Question 8.
Three consecutive integers are such that when they are taken in increasing order and multiplied by 2, 3 and 4 respectively, they add up to 74. Find these numbers.
Solution.

Question 9.
The ages of Rahul and Haroon are in the ratio 5 : 7. Four years later, the sum of their ages will be 56 years. What are their present ages ?
Solution.

Question 10.
The numbers of boys and girls in a class are in the ratio 7 : 5. The number of boys is 8 more than the number of girls. What is the total class strength ?
Solution. .

Question 11.
Baichung’s father is 26 years younger than Baichung’s grandfather and 29 years older than Baichung. The sum of the ages of all the three is 135 years. What is the age of each one of them ?
Solution.

Question 12.
Fifteen years from now Ravi’s age will be four times his present age. What is Ravi’s present age ?
Solution.

Question 13.
A rational number is such that when you multiply it by (frac < 5 > < 2 >) and add (frac < 2 > < 3 >) to the product, you get(-frac < 7 > < 12 >). What is the number ?
Solution.

Question 14.
Lakshmi is a cashier in a bank. She has currency notes of denominations ₹ 100, ₹ 50 and ₹ 10, respectively. The ratio of the number of these notes is 2 : 3 : 5. The total cash with Lakshmi is ₹ 4,00,000. How many notes of each denomination does she have ?
Solution.

Question 15.
I have a total of oft 300 in coins of denomination ₹ 1, ₹ 2 and ₹ 5. The number of ₹ 2 coins is 3 times the number of ₹ 5 coins. The total number of coins is 160. How many coins of each denomination are with me ?
Solution.

Hence, I have 80, 60, and 20 coins of denomination ₹ 1, ₹ 2 and ₹ 5 respectively.

Question 16.
The organizers of an essay competition decide that a winner in the competition gets a prize of ₹ 100 and a participant who does not win gets a prize of ₹ 25. The total prize money distributed is ₹ 3,000. Find the number of winners, if the total number of participants is 63.
Solution.

We hope the NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Ex 2.2 help you. If you have any query regarding NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Ex 2.2, drop a comment below and we will get back to you at the earliest.


2.2: Linear Equations in One Variable

Let the number be ‘a’.

According to the question,

(a – 1/2) × 1/2 = 1/8

a/2 – 1/4 = 1/8



a/2 = 1/8 + 1/4

a/2 = 1/8 + 2/8

a/2 = (1 + 2)/8

a/2 = 3/8

a = (3/8) × 2

So,

a = 3/4

Question 2. The perimeter of a rectangular swimming pool is 154 m. Its length is 2 m more than twice its breadth. What are the length and breadth of the pool?

Given that,

Perimeter of rectangular swimming pool = 154 m

Let the breadth of rectangle be ‘a’

Length of the rectangle = 2a + 2 We know that,

Perimeter = 2 × (length + breadth)

So,

2(2a + 2 + a) = 154

2(3a + 2) = 154

3a + 2 = 154/2

3a = 77 – 2



3a = 75

a = 75/3

a = 25

Therefore, Breadth = 25 m

Length = 2a + 2

= (2 × 25) + 2

= 50 + 2

Length = 52 m

Question 3. The base of an isosceles triangle is 4/3 cm. The perimeter of the triangle is 62/15 cm. What is the length of either of the remaining equal sides?

Base of isosceles triangle = 4/3 cm

Perimeter of triangle = 62/15

Let the length of equal sides of triangle be ‘a’.

So,

2a = (62/15 – 4/3)

2a = (62 – 20)/15

2a = 42/15

a = (42/30) × (1/2)

a = 42/30

a = 7/5

So, length of either of the remaining equal sides are 7/5 cm each.


Question 4. Sum of two numbers is 95. If one exceeds the other by 15, find the numbers.

Let one of the numbers be ‘a’.

Then, the other number becomes (a + 15) Given in the question,

Also given that,

a + (a + 15) = 95

2a + 15 = 95

2a = 95 – 15

2a = 80

a = 80/2

a = 40

So, First number = 40

And, other number is = (a + 15) = 40 + 15 = 55

Question 5. Two numbers are in the ratio 5 : 3. If they differ by 18, what are the numbers?

Let the two numbers be 𔃵a’ and 𔃳a’. So, according to the question,

5a – 3a = 18

2a = 18

a = 18/2

a = 19

Thus,

The first numbers is (5a) = 5 × 9 = 45

And another number (3a) = 3 × 9 = 27.

Question 6. Three consecutive integers add up to 51. What are these integers?

Let the three consecutive integers be ‘a’, ‘a + 1’ and ‘a + 2’. So, according to the question,

a + (a + 1) + (a + 2) = 51

3a + 3 = 51

3a = 51 – 3

3a = 48

a = 48/3

a = 16

So, the integers are



First integer will be (a) = 16

Second integer will be (a + 1) = 17

& third integer will be (a + 2) = 18

Question 7. The sum of three consecutive multiples of 8 is 888. Find the multiples.

Let the three consecutive multiples of 8 be 𔃸a’, 𔃸(a+1)’ and 𔃸(a+2)’. According to the question,

Given,

8a + 8(a + 1) + 8(a + 2) = 888

8 (a + a + 1 + a + 2) = 888 (Taking 8 as common)

8 (3a + 3) = 888

3a + 3 = 888/8

3a + 3 = 111

3a = 111 – 3

3a = 108

a = 108/3

a = 36

Thus, the three consecutive multiples of 8 are:

First no. = 8a = 8 × 36 = 288

Second no. = 8(a + 1) = 8 × (36 + 1) = 8 × 37 = 296

Third No. = 8(a + 2) = 8 × (36 + 2) = 8 × 38 = 304

Question 8. Three consecutive integers are such that when they are taken in increasing order and multiplied by 2, 3 and 4 respectively, they add up to 74. Find these numbers.

Let the three consecutive integers are ‘a’, ‘a+1’ and ‘a+2’. According to the question,

Given,

2a + 3(a + 1) + 4(a + 2) = 74

2a + 3a +3 + 4a + 8 = 74

9a + 11 = 74

9a = 74 – 11

9a = 63

a = 63/9

a = 7

Thus, the numbers are:

First integer. = a = 7

Second integer = a + 1 = 8

and Third integer = a + 2 = 9

Question 9. The ages of Rahul and Haroon are in the ratio 5:7. Four years later the sum of their ages will be 56 years. What are their present ages?

Let the ages of Rahul and Haroon be 𔃵a’ and 𔃷a’.

Four years later,

The ages of Rahul and Haroon will be (5a + 4) and (7a + 4) respectively. According to the question,

Given, (5a + 4) + (7a + 4) = 56

5a + 4 + 7a + 4 = 56

12a + 8 = 56



12a = 56 – 8

12a = 48

a = 48/12

a = 4

Therefore, Present age of Rahul = 5a = 5 × 4 = 20

And, present age of Haroon = 7a = 7 × 4 = 28

Question 10. The number of boys and girls in a class are in the ratio 7:5. The number of boys is 8 more than the number of girls. What is the total class strength?

Let the number of boys be 𔃷a’ and girls be 𔃵a’.

According to the question,

Given, 7a = 5a + 8

7a – 5a = 8

2a = 8

a = 8/2

a = 4

Therefore, Number of boys = 7 × 4 = 28

And, Number of girls = 5 × 4 = 20

Total number of students = 20 + 28 = 48

Question 11. Baichung’s father is 26 years younger than Baichung’s grandfather and 29 years older than Baichung. The sum of the ages of all the three is 135 years. What is the age of each one of them?

Let age of Baichung’s father be ‘a’.

Then, age of Baichung’s grandfather = (a + 26)

and, Age of Baichung = (a – 29) According to the question,

Given, a + (a + 26) + (a – 29) = 135

3a + 26 – 29 = 135

3a – 3 = 135

3a = 135 + 3

3a = 138

a = 138/3

a = 46

Age of Baichung’s father = a = 46

Age of Baichung’s grandfather = (a + 26) = 46 + 26 = 72

Age of Baichung = (a – 29) = 46 – 29 = 17

Question 12. Fifteen years from now Ravi’s age will be four times his present age. What is Ravi’s present age?

Let the present age of Ravi be ‘a’.

Fifteen years later, Ravi age will be (a+15) years. According to the question,

Given, a + 15 = 4a

4a – a = 15

3a = 15

a = 15/3

a = 5

Therefore, Present age of Ravi = 5 years.

Question 13. A rational number is such that when you multiply it by 5/2 and add 2/3 to the product, you get -7/12. What is the number?

Let the rational be ‘a’.

According to the question,

Given, a × (5/2) + 2/3 = -7/12

5(a/2) + 2/3 = -7/12

5(a/2) = -7/12 – 2/3

5(a/2) = (-7- 8)/12

5(a/2) = -15/12

5a/2 = -5/4

a = (-5/4) × (2/5)



a = – 10/20

a = -1/2

Therefore, the rational number will be -1/2.

Question 14. Lakshmi is a cashier in a bank. She has currency notes of denominations ₹100, ₹50 and ₹10, respectively. The ratio of the number of these notes is 2:3:5. The total cash with Lakshmi is ₹4,00,000. How many notes of each denomination does she have?

Let the numbers of notes of ₹100, ₹50 and ₹10 be 𔃲a’ , 𔃳a’ and 𔃵a’ respectively.

Value of ₹100 = 2a × 100 = 200a

Value of ₹50 = 3a × 50 = 150a

Value of ₹10 = 5a × 10 = 50a According to the question,

Given, 200a + 150a + 50a = 400000

400a = 400000

a = 400000/400

a = 1000

Numbers of ₹100 notes = 2a = 2000

Numbers of ₹50 notes = 3a = 3000

Numbers of ₹10 notes = 5a = 5000

Question 15. I have a total of ₹300 in coins of denomination ₹1, ₹2 and ₹5. The number of ₹2 coins is 3 times the number of ₹5 coins. The total number of coins is 160. How many coins of each denomination are with me?

Let number of ₹5 coins be ‘a’.

Then,

Number ₹2 coins = 3a

and, number of ₹1 coins = (160 – 4a) Now,

Value of ₹5 coins= a × 5 = 5a

Value of ₹2 coins = 3a × 2 = 6a

Value of ₹1 coins = (160 – 4a) × 1 = (160 – 4a)

According to the question,

Given, 5a + 6a + (160 – 4a) = 300

11a + 160 – 4a = 300

7a = 140

a = 140/7

a = 20

Number of ₹5 coins = a = 20

Number of ₹2 coins = 3a = 60

Number of ₹1 coins = (160 – 4a) = 160 – 80 = 80

Question 16. The organizers of an essay competition decide that a winner in the competition gets a prize of ₹100 and a participant who does not win gets a prize of ₹25. The total prize money distributed is ₹3,000. Find the number of winners, if the total number of participants is 63.

Let the numbers of winner be ‘a’

Then, the number of participant who didn’t win will be (63 – a)

Total money given to the winner = a × 100 = 100a

Total money given to participant who didn’t win = 25 × (63 – a)

According to the question,

Given, 100a + 25 × (63 – a) = 3000

100a + 1575 – 25a = 3000

75a = 3000 – 1575

75a = 1425

a = 1425/75

a = 19

So, the number of winners are 19.


Solve the following equations:

Ex 2.6 Class 8 Maths Question 1.

Solution:

Ex 2.6 Class 8 Maths Question 2.

Solution:

Ex 2.6 Class 8 Maths Question 3.

Solution:

Ex 2.6 Class 8 Maths Question 4.

Solution:

Ex 2.6 Class 8 Maths Question 5.

Solution:

Ex 2.6 Class 8 Maths Question 6.
The ages ofHari and Harry are in the ratio 5: 7. Four years from now the ratio of their ages will be 3 :4. Find their present ages.
Solution.
Let the present ages of Hari and Harry be 5x years and 7x years respectively.

∴ Present age of Hari =5 x 4 years = 20 years
∴ Present age of Harry =7 x 4 years = 28 years.

Ex 2.6 Class 8 Maths Question 7.
The denominator of a rational number is greater than its numerator by 8. If the numerator is increased by 17 and the denominator is decreased by 1, the number obtained is . Find the rational number.
Solution.
Let the numerator of the rational number be x. Then, the denominator of the rational number = x + 8.
∴ The rational number =
If the numerator is increased by 17 and the denominator is decreased by 1, the number becomes .

Hence, the required rational number = .

We hope the NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Ex 2.6 help you. If you have any query regarding NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Ex 2.6, drop a comment below and we will get back to you at the earliest.


NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Ex 2.3

NCERT Solutions for Class 8 Maths Chapter 2 Linear Equations in One Variable Exercise 2.3

Solve the following equations and check your results.
Ex 2.3 Class 8 Maths Question 1.
3x = 2x + 18
Solution:
We have 3x = 2x + 18
⇒ 3x – 2x = 18 (Transposing 2x to LHS)
⇒ x = 18
Hence, x = 18 is the required solution.
Check: 3x = 2x + 18
Putting x = 18, we have
LHS = 3 × 18 = 54
RHS = 2 × 18 + 18 = 36 + 18 = 54
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 2.
5t – 3 = 3t – 5
Solution:
We have 5t – 3 = 3t – 5
⇒ 5t – 3t – 3 = -5 (Transposing 3t to LHS)
⇒ 2t = -5 + 3 (Transposing -3 to RHS)
⇒ 2t = -2
⇒ t = -2 ÷ 2
⇒ t = -1
Hence t = -1 is the required solution.
Check: 5t – 3 = 3t – 5
Putting t = -1, we have
LHS = 5t – 3 = 5 × (-1)-3 = -5 – 3 = -8
RHS = 3t – 5 = 3 × (-1) – 5 = -3 – 5 = -8
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 3.
5x + 9 = 5 + 3x
Solution:
We have 5x + 9 = 5 + 3x
⇒ 5x – 3x + 9 = 5 (Transposing 3x to LHS) => 2x + 9 = 5
⇒ 2x = 5 – 9 (Transposing 9 to RHS)
⇒ 2x = -4
⇒ x = -4 ÷ 2 = -2
Hence x = -2 is the required solution.
Check: 5x + 9 = 5 + 3x
Putting x = -2, we have
LHS = 5 × (-2) + 9 = -10 + 9 = -1
RHS = 5 + 3 × (-2) = 5 – 6 = -1
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 4.
4z + 3 = 6 + 2z
Solution:
We have 4z + 3 = 6 + 2z
⇒ 4z – 2z + 3 = 6 (Transposing 2z to LHS)
⇒ 2z + 3 = 6
⇒ 2z = 6 – 3 (Transposing 3 to RHS)
⇒ 2z = 3
⇒ z = (frac < 3 >< 2 >)
Hence z = (frac < 3 >< 2 >) is the required solution.
Check: 4z + 3 = 6 + 2z
Putting z = (frac < 3 >< 2 >), we have
LHS = 4z + 3 = 4 × (frac < 3 >< 2 >) + 3 = 6 + 3 = 9
RHS = 6 + 2z = 6 + 2 × (frac < 3 >< 2 >) = 6 + 3 = 9
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 5.
2x – 1 = 14 – x
Solution:
We have 2x – 1 = 14 – x
⇒ 2x + x = 14 + 1 (Transposing x to LHS and 1 to RHS)
⇒ 3x = 15
⇒ x = 15 ÷ 3 = 5
Hence x = 5 is the required solution.
Check: 2x – 1 = 14 – x
Putting x = 5
LHS we have 2x – 1 = 2 × 5 – 1 = 10 – 1 = 9
RHS = 14 – x = 14 – 5 = 9
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 6.
8x + 4 = 3(x – 1) + 7
Solution:
We have 8x + 4 = 3(x – 1) + 7
⇒ 8x + 4 = 3x – 3 + 7 (Solving the bracket)
⇒ 8x + 4 = 3x + 4
⇒ 8x – 3x = 4 – 4 [Transposing 3x to LHS and 4 to RHS]
⇒ 5x = 0
⇒ x = 0 ÷ 5 [Transposing 5 to RHS]
or x = 0
Thus x = 0 is the required solution.
Check: 8x + 4 = 3(x – 1) + 7
Putting x = 0, we have
8 × 0 + 4 = 3(0 – 1) + 7
⇒ 0 + 4 = -3 + 7
⇒ 4 = 4
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 7.
x = (frac < 4 >< 5 >) (x + 10)
Solution:
We have x = (frac < 4 >< 5 >) (x + 10)
⇒ 5 × x = 4(x + 10) (Transposing 5 to LHS)
⇒ 5x = 4x + 40 (Solving the bracket)
⇒ 5x – 4x = 40 (Transposing 4x to LHS)
⇒ x = 40
Thus x = 40 is the required solution.
Check: x = (frac < 4 >< 5 >) (x + 10)
Putting x = 40, we have
40 = (frac < 4 >< 5 >) (40 + 10)
⇒ 40 = (frac < 4 >< 5 >) × 50
⇒ 40 = 4 × 10
⇒ 40 = 40
LHS = RHS
Hence verified.

Ex 2.3 Class 8 Maths Question 8.
(frac < 2x >< 3 >) + 1 = (frac < 7x >< 15 >) + 3
Solution:
We have (frac < 2x >< 3 >) + 1 = (frac < 7x >< 15 >) + 3
15((frac < 2x >< 3 >) + 1) = 15((frac < 7x >< 15 >) + 3)
LCM of 3 and 15 is 15
(frac < 2x >< 3 >) × 15 + 1 × 15 = (frac < 7x >< 15 >) × 15 + 3 × 15 [Multiplying both sides by 15]
⇒ 2x × 5 + 15 = 7x + 45
⇒ 10x + 15 = 7x + 45
⇒ 10x – 7x = 45 – 15 (Transposing 7x to LHS and 15 to RHS)
⇒ 3x = 30
⇒ x = 30 ÷ 3 = 10 (Transposing 3 to RHS)
Thus the required solution is x = 10

Ex 2.3 Class 8 Maths Question 9.
2y + (frac < 5 >< 3 >) = (frac < 26 >< 3 >) – y
Solution:

Ex 2.3 Class 8 Maths Question 10.
3m = 5m – (frac < 8 >< 5 >)
Solution:
We have


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