Question

The surface area of the frustum cone is given its base radius, R = 12 m and top radius, r = 9 m. The height of the cone is 4 m. Find the slant height of the cone.

• A. $2\sqrt{7}$ cm
• B. $\sqrt{5}$ cm
• C. 5 cm
• D. $2\sqrt{5}$ cm

Answer 1

Answer: (C)

5 cm

Slant height of a cone = $\sqrt{(R-r{)}^2+h^2}$
= $\sqrt{(12-9{)}^2+4^2}$
= $\sqrt{(3{)}^2+16}$
= $\sqrt{9+16}$
= $\sqrt{25}$ cm
= 5 cm