Question

The curved surface area of a hemisphere is 77 cm2. Radius of the hemisphere is?

Answer 1

$$\begin{gathered} \mathrm{Let}\mathrm{r}\mathrm{be}\mathrm{the}\mathrm{radius}\mathrm{of}\mathrm{the}\mathrm{hemisphere}. \\ \mathrm{Now},\mathrm{CSA}\mathrm{of}\mathrm{hemisphere}=77{\mathrm{cm}}^2 \\ \Rightarrow 2{\mathrm{\pi r}}^2=77 \\ \Rightarrow 2\times \frac{22}{7}\times {\mathrm{r}}^2=77 \\ \Rightarrow {\mathrm{r}}^2=\frac{77\times 7}{44} \\ \Rightarrow {\mathrm{r}}^2=\frac{49}{4} \\ \Rightarrow \mathrm{r}=\frac{7}{2}=3.5 \\ \mathrm{So},\mathrm{radius}\mathrm{of}\mathrm{the}\mathrm{hemisphere}=3.5\mathrm{cm} \end{gathered}$$