P, Q and R are three points on the circumference of a circle such that QR is a diameter and PQ = PR. If the radius of the circle is 7 cm, then the length of PQ is:

$7\sqrt{2}$ cm

We have,

The radius of the circle = 7 cm.

We know that,

∠QPR = 90° ( angle in a semicircle opposite to diameter is always 90°)

So ∆PQR is a right angle triangle

PQ = QR/√2    (In an isosceles right triangle the smaller side is (1/√2) of hypotenuse)

= PQ = 14/√2

= PQ = 7√2