Question

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

${\displaystyle [\text{Assume}\pi =\frac{22}{7}]}$

Answer 1

Radius (r) of sphere = ${\displaystyle \frac{\text{Diameter}}{2}}$

= ${\displaystyle \left(\frac{21}{2}\right)cm}$

= 10.5 cm

Surface area of sphere = 4πr²

= ${\displaystyle [4\times \frac{22}{7}\times {\left(10.5\right)}^2]c{m}^2}$

= 1386 cm²

Therefore, the surface area of a sphere having diameter 21 cm is 1386 cm².