Find the surface area of a sphere of diameter 21 cm.
Given,
Diameter of sphere (d) = 21 cm
Radius of sphere (r) = Diameter2=212\dfrac{\text{Diameter}}{2} = \dfrac{21}{2}2Diameter=221 = 10.5 cm
By formula,
Surface area of a sphere (A) = 4πr2
A=4×227×(10.5)2=4×227×10.5×10.5=4×22×1.5×10.5=1386 cm2.A = 4 \times \dfrac{22}{7} \times (10.5)^2 \\[1em] = 4 \times \dfrac{22}{7} \times 10.5 \times 10.5 \\[1em] = 4 \times 22 \times 1.5 \times 10.5 \\[1em] = 1386 \text{ cm}^2.A=4×722×(10.5)2=4×722×10.5×10.5=4×22×1.5×10.5=1386 cm2.
Hence, the surface area of a sphere = 1386 cm2.
