The curved surface area of a right circular cone of height 12 cm and base diameter 10 cm is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(65\pi\) cm2
The curved surface area of a cone is \(\pi r l\), where \(l\) is the slant height. The height, the radius and the slant height form a right triangle, so \(l=\sqrt{h^2+r^2}\).
Radius \(r=10\div2=5\) cm, height \(h=12\) cm
Slant height \(l=\sqrt{12^2+5^2}=\sqrt{169}=13\) cm
Curved surface area, with the slant height (not the height) in the formula: \(\pi\times5\times13=65\pi\) cm2