Question

A right angled sector of radius r сm is rolled up into a cone in such a way that the two binding
radii are joined together. Then the curved surface area of the cone is
​

Answer 1

Here OAB is the required sector of radius r , AB = 90/180 × 22/7 × r = 22/7× r/2

Now PQR is the cone formed with l= r ,

base perimetre = AB.

So, 2×22/7 × R = 22/7×r/2

4R= r

R= r/4

So , C.S.A of cone = 22/7× r/4×r = 22/7×r^2/4.