Solution:
Construction: Join AC and BD
Proof:
(i) We know that in a cyclic quadrilateral, the exterior angle is equal to opposite interior angle.
Therefore, ∠PAC=∠PDB ……….(i) Proved
Similarly, ∠PCA=∠PBD …………(ii)
In view of (i) and (ii)
ΔPAC∼ΔPAB (AA test of similarity)
∴PAPD=PCPB (since ΔPAC∼ΔPAB) & corresponding sides of similar triangles are proportional
∴PA×PB=PC×PD
Hence proved.