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

A = πr^{2}

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

To work out the shaded area shown below, we must work out the area of the outer circle and subtract the area of the inner circle.

**Example**

Calculate the shaded area in cm^{2} between the two circles shown below.

Give your answer to **3 significant figures**.

**Answer**

Area of outer circle = π x 9^{2} = 81π

Area of inner circle = π x 8^{2} = 64π

**Shaded area** = 81π - 64π = 17π = **53.38 ****cm ^{2}**

^{ }

= **53.4 cm ²** (3 s.f.)

Let's have a go at some questions.