## Definition

**Quadrangle**It is a four-sided polygon.

Quadrangle *A B C D*

In a quadrangle, two sides or two nonconsecutive angles are called opposites.

## Elements

In the figure below, we have:

Quadrangle *A B C D*

**Vertices:** A, B, C, and D.** Sides:** **Diagonals:**

Internal angles or angles of

ABCD quad: .

Comments:

Every quad has two diagonals.

The perimeter of a quadrilateral ABCD is the sum of the measurements on its sides, ie AB + BC + CD + DA.

## Concave and Convex

The quads can be convex or concave. A quad is **convex** when the line joining two consecutive vertices does not find the side formed by the two other vertices.

Convex Quad

Concave Quad