In a circle, AB is a the diameter and CD is a chord. AB and CD produced meet at a point P, outside the circle. If PD = 15.3 cm, CD = 11.9 cm and AP = 30.6 cm, then the radius of the circle is is:

8.5 cm

By using concept ,

PD × PC = PB × PA

15.3 × ( 15.3 + 11.9 ) = PB × 30.6

15.3 × 27.2  = PB × 30.6

PB = 13.6 cm

Now,

AB = AP - PB

= 30.6 - 13.6

= 17

Radius of the circle = \(\frac{AB}{2}\)

= \(\frac{17}{2}\)

= 8.5 cm