Question

The area of a circle is 49 π cm². Its circumference is
(a) 7 π cm
(b) 14 π cm
(c) 21 π cm
(d) 28 π cm

Answer 1

(b) 14π cm
Let the radius be r cm.
We know:
Area of a circle$=\mathrm{\pi }{r}^2$
Thus, we have:
$$\begin{gathered} \mathrm{\pi }{r}^2=49\mathrm{\pi } \\ \Rightarrow r^2=49 \\ \Rightarrow r=\sqrt{49} \\ \Rightarrow r=7 \end{gathered}$$

Now,
Circumference of the circle$=2\mathrm{\pi r}$
$$\begin{gathered} =\left(2\times \frac{22}{7}\times 7\right)\mathrm{cm} \\ =14\mathrm{\pi }\mathrm{cm} \end{gathered}$$