Question 68

The area of the base of a right circular cone is $$\frac{1408}{7} cm^2$$and its height is 6 cm. Taking $$\pi = \frac{22}{7}$$, the curved surface area of the cone is:

Solution

Area of base = $$\pi r^2=\frac{1408}{7}$$

=> $$\frac{22}{7}\times r^2=\frac{1408}{7}$$

=> $$r^2=\frac{1408}{22}=64$$

=> $$r=\sqrt{64}=8$$ cm

Also, height = $$h=6$$ cm

Thus, slant height of cone = $$l=\sqrt{r^2+h^2}=\sqrt{64+36}=\sqrt{100}=10$$ cm

$$\therefore$$ Curved surface area of cone = $$\pi rl$$

= $$\frac{22}{7}\times8\times10=\frac{1760}{7}$$ $$cm^2$$

=> Ans - (C)

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