Question

If A is the area and C be the circumference of a circle, then its radius is
(a) $\frac{A}{C}$ (b) $\frac{2A}{C}$ (c) $\frac{3A}{C}$ (d) $\frac{4A}{C}$

Answer 1

Let r be the radius of the circle. Then
$$\begin{gathered} A=\pi r^{2}andC=2\pi r \\ \Rightarrow \frac{A}{C}=\frac{\pi r^2}{\mathit{2}\pi r} \\ \Rightarrow \frac{A}{C}=\frac{r}{\mathit{2}} \\ \Rightarrow r=\frac{2A}{C} \end{gathered}$$
Hence, the correct option is (b).