Quadrilaterals

A quadrilateral is a plane figure bounded by four straight sides having four angles. Any two opposite angles may be joined by a straight line called a diagonal.

A diagonal is a straight line that connects the opposite corners of a quadrilateral. There are two diagonals and they divide a quadrilateral into two triangles. Each triangle has an angle sum of 180°. Therefore, the total angle sum of the quadrilateral is 360°.

A quadrilateral may be regular or irregular. A regular quadrilateral has sides of equal lengths and all its angles of equal size, while an irregular quadrilateral has sides of different lengths and angles of different sizes.