The diameter of a circle is a line which joins two points on the circle and also passes through the centre of the circle. AB is a diameter of the circle; C is its centre. Express the diameter of the circle (d) in terms of its radius (r).

**Answer:**

It is given to us that AB is the diameter of the circle and C is the centre of the circle.

We know that AC, BC and PC are radii of the circle.

Therefore,

Diameter of the circle = d = AC + BC = r + r = 2r