Find the Area of Part Circles

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

Recap

The formula for the area, A, of a circle in terms of its radius, r, is given by:

A = π r²

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 area of the quarter-circle below.

Answer

We can see that we have one quarter of a circle and that the radius is 4 cm.

Area of full circle = π x r² 

A =  π x 4² 

A = 50.27548.....

This is the area of the whole circle!

We only want 1/4 of the area.

So, we divide by 4.

Area of quarter-circle = 50.27548... ÷ 4

Area = 12.6 cm²  (to 1 decimal place)

Let's have a go at some questions!