A circle is drawn through the four corners of a rectangle whose sides are 16 cm and 12 cm. Find the area of the circle in ${\text{cm}}^2$. Take π = 3.14.

The rectangle's diagonal is a diameter of the circle, and it measures √$(16^2+12^2)=$ √400 = 20 cm. So $r=10$ cm and the area = $3.14\times 100=314{\text{cm}}^2$. (Taking the 20 cm diagonal as the radius gives $1256{\text{cm}}^2$; $192{\text{cm}}^2$ is the rectangle's own area.)