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

A = πr^{2}

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 sig. figs.

**Answer**

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

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

**Shaded area** = 81π - 64π = 17π = **53.4 ****cm ^{2}**

^{ }(3 s.f.)