Question 61

What is the total surface area of a cone which has a radius of 21 cm and a height of 28 cm? (Take $$\pi = \frac{22}{7}$$)

Solution

r = radius of cone = 21 cm

h = height of cone = 28 cm
total surface area of a cone = $$\pi\ \times\ r\times\left(r+\sqrt{\ r^2+h^2}\right)$$

= $$\frac{22}{7}\times\ 21\times\left(21+\sqrt{\ \left(21\right)^2+\left(28\right)^2}\right)$$

= $$22\times3\times\left(21+\sqrt{\ 441+784}\right)$$

= $$66\times\left(21+\sqrt{1225\ }\right)$$

= $$66\times\left(21+35\right)$$

= $$66\times56$$

= 3696 $$cm^2$$

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