Find the Perimeter of Part Circles

In this activity, we will calculate the perimeter of parts of circles.

Recap

For this activity, we need to use the formula for the circumference, C, of a circle:

C = 2 π r

In this activity, we will use the π symbol on our calculators in our calculations.  If you do not have a scientific calculator, you can always use one online.

Let's look at a typical question!

Example

Calculate the perimeter of the quarter-circle below.

Answer

We can see that we have one quarter of a circle and that the radius is 2 cm

First, we need to find the circumference of the full circle.

C of full circle = 2 x π x r 

C = 2 x  π x 2 

A = 12.566.....

This is the circumference of the whole circle!

We only want 1/4 of the circumference.

We divide by 4

Circumference of quarter-circle = 12.566... ÷ 4

Circumference = 3.14 cm

To get the perimeter = 3.14 cm + 2 cm + 2 cm

Perimeter = 7.14 cm

Let's have a go at some questions!