Question

Circle with O as the centre. RS is a tangent to the circle. Calculate:

a) the radius of the circle, in cm
b) the length of OR

Answer 1

It is a right triangle.

So, using Pythagorean theorem: OS² = OR² - RS²

OR = r (radius) + 8

OS = r

RS = 16

=> r² = (r+8)² - 16²

r² = r² + 16r + 64 - 256

r² = r² + 16r - 192

16r = 192

r = 192 / 16 = 12cm²

a) 12 cm²

b) 12 + 8 = 20 cm²