What is the total surface area of a cone which has a radius of 21 cm and a height of 28 cm? (Take $π =\frac{22}{7}$)
Answer & explanation
Correct answer: option 1
We know that,
Total surface area of cone = πr (l + r)
l2 = r2 + h2
We have,
Radius = r = 21 cm
Height = h = 28 cm
= l2 = 212 + 282
= l2 = 441 + 784
= l = \(\sqrt {1225}\)
= l = 35
Total surface area of cone = \(\frac{22}{7}\) × 21 × (21 + 35) = 22 × 3 × 56 = 3696 cm2