A right angled sector of radius r cm 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

Explanation:

⇒ Circumference of sectors =πr\2

⇒ Circumference of base of cone of radius =2πr1

πr\2=2πr1

r1=r\4

∴ Radius of cone =r\4

Curved surface area of cone =πr1l

l = slant height

l = r

∴ Surface area of cone

π×r\4×r⇒πr^2\4