The height of a right circular cone is 4cm. The radius of its base is...
MATHEMATICS
WAEC 2002
The height of a right circular cone is 4cm. The radius of its base is 3cm. Find the curved surface area
- A. \(9\pi cm^2\)
- B. \(15\pi cm^2\)
- C. \(16\pi cm^2\)
- D. \(20\pi cm^2\)
Correct Answer: B. \(15\pi cm^2\)
Explanation
Curved surface area or a cone \(=\pi rl\)
from the information \(l^2 = 4^2 + 3^2 = 16+9\\
l = \sqrt{25} = 5; ∴ C.S.A\hspace{1mm} = \frac{22}{7}\times 3 \times 5\\
Since \frac{22}{7}=\pi ∴ C.S.A\hspace{1mm} =\hspace{1mm}15\pi\)
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