# In a circle, two chords AB and CD intersect at a point P inside the circle. Prove that(a) ΔPAC ~ ΔPDB (b) PA • PB = PC • PD.

Given: AB and CD are chords of the circle, intersecting at point P.

(a). To Prove: ∆PAC ∆PDB

Proof: In ∆PAC and ∆PDB,

APC = DPB [ they are vertically opposite angles]

CAP = PDB [ angles in the same segment are equal]

Thus, by AA-similarity criteria, we can say that,

∆PAC ∆PDB

Hence, proved.

(b). To Prove: PA × PB = PC × PD

Proof: As already proved that ∆PAC ∆PDB

We can write as,

By cross-multiplying, we get

PA × PB = PC × PD

Hence, proved.

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