Question

Find the surface area of a sphere of diameter $21cm$.

Answer 1

Step 1: Find the radius of the sphere.

Let $r$ be the radius of the sphere and $d$ be the diameter.

Since, $r=\frac{d}{2}$

$\therefore r=\frac{21}{2}cm$

Step 2: Find the surface area of the sphere.

Surface area of the sphere of radius $r$ $=4{\mathrm{\pi r}}^2$

$=4\times \frac{22}{7}\times {\left(21\right)}^2$

$=5544c{m}^2$

Hence, the surface area of the sphere is $5544c{m}^2$.