A sector containing of angle 120degree is cut off from a circle of radius 21 cm and folded into a cone. find C.S.A of cone
Answers
Step-by-step explanation:
Let r be the base radius of the cone.
Angle of the sector, θ=120
o
Radius of the sector, R=21cm
When the sector is folded into a right circular cone, we have circumference of the base of the cone= Length of the arc
⇒2πr=
360
o
θ
×2πR
⇒r=
360
o
θ
×R
Thus, the base radius of the cone, r=
360
o
120
o
×21=7cm
Also, the slant height of the cone,
l= Radius of the sector
Thus, l=R ⇒ l=21cm
Now, the curved surface area of the cone,
CSA=πrl
=
7
22
×21=462
Thus, the curved surface area of the cone is 462sq.cm
solution
Answer:
Let r be the base radius of the cone.
Angle of the sector, θ=120
o
Radius of the sector, R=21cm
When the sector is folded into a right circular cone, we have circumference of the base of the cone= Length of the arc
⇒2πr=
360
o
θ
×2πR
⇒r=
360
o
θ
×R
Thus, the base radius of the cone