### Quadrilaterals

A **quadrilateral** is a plane figure bounded by four straight sides.

This quadrilateral is called a **convex quadrilateral** because none of its four interior angles is a reflex angle.

This quadrilateral is called a **non-convex quadrilateral** because one of its interior angles is a reflex angle.

A quadrilateral has two **diagonals** that join opposite vertices.

Both diagonals of a convex quadrilateral are inside the quadrilateral.

One of the diagonals of a non-convex quadrilateral is outside the quadrilateral.