When we found unknown trigonometric function or trigonometric function of some unknown function in at least one member of an equation we say this equation is trigonometric
1) sin x + cos x = and sin 2x = cos2 x are trigonometric equations.
2) x + (tg 30 °). x2 e x + sen 60º = they are not trigonometric equations.
We say that r is root or solution of the trigonometric equation f (x) = g (x) if r is a domain element of f and g and if f (r) = g (r) is true.
In the equation sen x - sen = 0, for example, the numbers are some of its roots and the numbers they are not.
The set s of all the roots of the equation is your solution set or True set. Almost all trigonometric equations, when properly treated and transformed, can be reduced to at least one of the following three equations:
sen x = sen a
cos x = cos a
tg x = tg a
These are the elementary trigonometric equations or fundamental trigonometric equations.Next: Resolution of the 1st Fundamental Equation