Power of a point with respect to a circle

Posted November 29th, 2008 by Structure

Two lines by a point P outside a circle cut in A,B respectively in C and D. Then

$PA*PB=PC*PD=TP^2$

$\triangle PAC\sim\triangle PDB$

as $\angle PBD=\angle PCA\:\:;\angle PDB=\angle PAC$

$\frac{PA}{PD}=\frac{PC}{PB}$

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