Q. 5

In the given figure, O is a centre of a circle. If OAB = 40° and C is a point on the circle, then ACB = ?


A. 40o

B. 50o

C. 80o

D. 100o

Answer :

In Δ AOB OA = OB( radius)


OAB = OBA (Angles opposite to equal sides are equal)


OBA = 40


By angle sum property


OAB + OBA + AOB = 180°


AOB = 180° – OAB – OBA


AOB = 180° – 40° – 40° = 100°


We know that


2 ×ACB = AOB (The angle subtended by an arc at the center is twice the angle subtended by the same arc on any point on the remaining part of the circle).


2 ×ACB = 100°


ACB =


ACB = 50

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