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 \(20\pi cm^2\)
waec 2002mathematics

The correct answer is B. \(15\pi cm^2\)

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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