"Tangent AB and secant ACD are drawn to circle O from an external point A, AB = 8, and AC = 4. What is the length of CD?"

Question

Find the length of CD.

Answer 1

There is a principle which states that

AD/AB = AB/AC

Plugging the known values we have

AD/8 = 8/4

AD= 64/4 = 16

CD = 16 - 4 = 12

CD = 12