In the given figure, O is the centre of the circle. Its two chords AB and CD intersect each other at the point P within the circle. If AB = 15 cm, PB = 9 cm, CP = 3 cm, then find the length of PD.

18 cm

We know that,

AP × PB = CP × PD

We have,

AB = 15 cm

PB = 9 cm and CP = 3 cm

According to the question,

AP = AB - PB 

= AP = 15 - 9 = 6 cm

According to the formula

AP × PB = CP × PD

= 6 × 9 = 3 × PD

PD = 18