Secant-Tangent Theorem states: If a secant PA and tangent PC meet a circle at the respective points A, B, and C (point of contact),

then (PC)^2 = (PA)(PB).

My work so far on the proof:

Given circle O with secant PA and tangent PC which meet circle O at A, B, and C.

Draw chords AC and BC.

Angle CPA is congruent to Angle CPB.

Angle PCA is congruent to Angle PBC (both angles intercept arc AC).

Triangle ACP ~ Triangle DBP by the Angle-Angle Similarity Criterion.

Now, this is where I am stuck. I know the two triangles are similar. My hunch is to manipulate the relations of corresponding parts of similar triangles to get to what I want to prove that (PC)^2 = (PA)(PB).

Will the Inscribed Angle Theorem help any?

(Inscribed Angle Theorem: The measure of an inscribed angel of a circle equals 1/2 that of its intercepted arc.)

Any help is greatly appreciated! Thank you for your time.