Parts or elements of a quadrilateral are discussed here.

ABCD is a quadrilateral with four sides namely AB, BC, CD and DA.

It has four vertices namely A, B, C and D. The angle between two adjacent sides is an angle of the quadrilateral. So, a quadrilateral has four angles that is, ∠DAB, ∠ABC, ∠BCD and ∠CDA.

A line segment joining a pair of opposite vertices is called a diagonal. So, there are two diagonals namely AC and BD.

A quadrilateral may have some relations between its sides and angles. On the basis of these relations, quadrilaterals are classified and given different names.

Parallel Lines.

Perpendicular Lines.

Construction of Perpendicular Lines by using a Protractor.

Sum of Angles of a Quadrilateral.