Question

If the length of tangent line is 4 cm drawn from any point, 10 cm away from the center of circle, then what will be the radius of that circle ?

Answer 1

PQ is the tangent drawn an circle from external point Q and OP is radius of circle.

So ∠OPQ = 90° 

From ∆OPQ

OQ² =PQ² + OP² (By Pythagoras theorem)

10² = 4² + OP²

OP² = 10² – 4²

= 100 – 16

= 84

OP = \(\sqrt { 84 }\) cm

OP = 2\(\sqrt { 21 }\) cm