From an external point P, a tangent PQ is drawn to a circle, with the centre O, touching the circle at Q. If the distance of P from the centre is 13 cm and length of the tangent PQ is 12 cm, then the radius of the circle is:

5 cm

Radius of the circle intersect at tangent PQ on the circumference of the circle and for 90º angle.

By using pythagoras theorem ,

PO² = PQ² + OQ²

13² = 12² + OQ²

OQ² = 169 - 144

OQ = 5 cm