This is circle based question from Chapter name- circles

Topic – Angle properties of circles

Chapter number- 15

In this question we have figure of circle with constructions and we have to find the value of x using basic properties of circles.

ICSE Avichal publication

Understanding ICSE Mathematics

Question no 2

∠AOC + ∠COB = 180

^{o}135

^{o}+ ∠COB = 180^{o}∠COB = 180

^{0}– 135^{o}= 45^{o}Now arc BC Subtends reflex ∠COB at the centre and ∠ CDB at the remaining part of the circle.

∠COB = 2 ∠CDB

∠CDB = ½ ∠COB

= ½ × 45

^{o}= 45^{o}/2 = 22 1/2^{o}