From a point Q, the length of the tangent to a circle is 40 cm an

| From a point Q, the length of the tangent to a circle is 40 cm and the distance of Q from the centres is 41 cm. The radius of the circle is _______ cm.

A. 9

B. 7

C. 8

D. 10

Please scroll down to see the correct answer and solution guide.

Right Answer is: A

SOLUTION

OB = Radius of the circle

OQ = 41 cm and BQ = 40 cm

ΔOBQ is right angled triangle at B

OQ² = OB² + BQ²

⇒ 41² = 40² + OB²

⇒ OB²= 1681 - 1600

⇒ OB²= 81

∴ OB = 9 cm = Radius of the circle