A right angle sector of radius r cm is rolled up into a cone by joining along the radius. Then the curved surface area of the cone is?
Answer & explanation
Correct answer: option 1
R = radius of the base of cone
r = radius of circle
Circumference of base of cone= \(2 \pi R = \frac{2 \pi r}{4}\)
Therefore, radius of base (R) = \(\frac{r}{4}\)
slant height = r
C.S.A. = \(\pi \)Rl = \(\pi \)(\(\frac{r}{4}\))r
= \(\frac{\pi}{4} r^2\)