One of the most important and exam oriented question from Chapter name- circles

Topic – Angle properties of circles

Chapter number- 15

It is given that AD is a diameter of a circle with centre O and AB is tangent at A.

C is a point on the circle such that DC produced intersects the tangent of B.

Also ∠ABC = 50°, now we have to find ∠AOC.

ICSE Avichal publication

Understanding ICSE Mathematics

Question 19

Solution:Given AB is tangent to the circle at A and OA is radius, OA ⊥ AB

In ∆ABD

<DAB+<ABD+<ADB=180

90+50+<ADB=180

<ADB=40

<AOC=<OCD+<ODC=40+40=80