In the diagram of circle O, tangent PB is drawn as is secant PAC . We wish to prove the Secant/Tangent Length Theorem, i. e. PAPC  PB2 .
(a) Explain why PAB is similar to PBC (i. e. explain which two angles pairs must be congruent and why).
(b) Set up a proportion involving PA, PB, and PC based on the similar triangles and rewrite it in product form. Draw the two similar triangles separately and in the same orientation to help.