# Chapter 15 – Quadrilaterals – R S Aggarwal Solutions for class 8

Quadrilateral is a polygon bounded by four line segments AB, BC, CD and DA.

Here the points A, B, C, D are known as vertices.

∠A,∠B, ∠C and ∠D are angles of Quad ABCD

The lines AC and BD are diagonals of Quad ABCD

(a) Adjacent sides: Two sides of quadrilateral is said to be adjacent sides, if they have a common end point. In the above figure (AB, BC), (BC, CD), (CD, DA) and (DA, AB) are adjacent sides.

(b) Opposite sides: Two sides of quadrilateral is said to be opposite sides, if they do not have a common end point. In the above figure (AB, CD) and (DA, BC) are opposite sides.

(c) Adjacent angles: Two angles of a quadrilateral are called adjacent angles if they have a common side as an arm. In the above figure (∠A,∠B),∠B,∠C,∠C,∠D and (∠D,∠A) are pairs of adjacent angles.

(d) Opposite angles: Two angles of a quadrilateral are called opposite angles which are not adjacent. In the above figure (∠A,∠C) and (∠D,∠B) are pairs of opposite angles.

(e) Angle sum property of a quadrilateral: sum of the angles of a quadrilateral is 360?