Question

a sector containing an angle of 120 degree cut off from a circle of radius 21 cm and folded into a cone .find the curved surface area of the cone.

Answer 1

Answer:

Step-by-step explanation:

CSA of cone is πr(L+r)

Now put the value and get the answer

Answer 2

Answer:

462sq.cm

Step-by-step explanation:

angle of the sector =theta = 120°

radius of the sector R =21cm

when the sector is folded, we have

length of the arc = circumference of base of cone

slant height of cone = 21 cm

so, the formula is

theta

---------- ×2πR= 2πr

360°

120°

------- × 2πR = 2πr

360°

1

---- × 21 ( R) = r ( cancelling 2π on both sides )

3

r = 7 cm

CSA of Cone = πrl sq units

= 22

------ × 7 × 21

7

= 462 cm^2