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 (d) in terms of its radius (r).

Answer 1

In the given figure, AB is the diameter and CP is the radius.

AB = AC + CB

AC= CB =CP [Radii of the same circle]

$\Rightarrow$AB = CP+CP

$\Rightarrow$AB = 2CP

Given, diameter AB= d and radius CP = r

$\therefore$ d =2r