Examples
Ex 1:

The circumference of a circle of a radius 1.4 cm is

Sol:
Put r = 1.4 cm in circumference = 2πr
= 44 ✗ 0.2
= 8.8 cm
Ex 2:

If the perimeter of a semicircle is 144 cm. Find its radius.

Sol:
circumference + diameter = perimeter
πr + 2r = 144 cm
Ex 3:

The moon is about 384000 km from the earth and its path around the earth is nearly circular. Find the circumference of the path described, by the moon in one complete revolution about the earth (π = 3.14).

Sol:
Radius of the orbit = 384000 km
Distance covered = 2πr cm
= 2 ✗ 3.14 ✗ 384000
=
= 628 ✗ 3840
Distance covered in one complete revolution = 2411520 km