Question

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

Answer 1

Since $C$ is center of circle, $CA,CB,CP$ are radius.

$\therefore CA=CB=CP=r$

Now,$AB$ is diameter of circle.

$AB=AC+BC$

$d=r+r=2r$