JEE Advance - Mathematics (2001 - No. 22)
Let PQ and RS be tangents at the extremities of the diameter PR of a circle of radius r. If PS and RQ intersect at a point X on the circumference of the circle, then 2r equals
$$\sqrt {PQ.\,RS} $$
(PQ + RS) / 2
2 PQ. RS/(PQ + RS)
$$\sqrt {\left( {P{Q^2} + \,R{S^2}} \right)} \,\,/2$$