In the following figure, two circles with centres A and B touch each other at the point C. If AC = 8 cm and AB = 3 cm, find the area of the shaded region.
Area of the shaded region can be calculated as shown below,
Area of the shaded region = Area of circle with radius AC − area of circle with radius BC
We have given radius of the outer circle that is 8 cm but we don’t know the radius of the inner circle.
We can calculate the radius of the inner circle as shown below,
$B C=A C-A B$
$\therefore B C=8-3$
$\therefore B C=5$
$\therefore$ Area of the shaded region $=\pi \times 8 \times 8-\pi \times 5 \times 5$
$\therefore$ Area of the shaded region $=\pi \times 64-\pi \times 25$
$\therefore$ Area of the shaded region $=\pi \times 39$
Substituting $\pi=\frac{22}{7}$ we get,
$\therefore$ Area of the shaded region $=\frac{22}{7} \times 39$
$\therefore$ Area of the shaded region $=122.57$
Therefore, area of the shaded region is $122.57 \mathrm{~cm}^{2}$.