Theorem 2. If PAB is a secant to a circle intersecting it at A and B and PT is a tangent then PA.PB = PT2.
Given: - PAB is secant intersecting the circle with centre O at A and B and a tangent PT at T.
To Prove: - PA.PB = PT2
Construction: - is drawn OA, OP and OT are joined.
Proof: - PA = PM – AM
PB = PM + MB
Also
PM2 = OP2 - OM2 [Pythagoras theo.]
and AM2 = OA2 - OM2 [Pythagoras theo.]
PA.PB = PT2 [Pythagoras theo.]
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