Q.The slant height of a frustum of cone is 4cm and the perimeters(circumference) of its circular ends are 18cm and 6cm.Find the curved surface area of the frustum.
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Answer:
Given,
Perimeter of top circle having radius (r) is
2πr=6 cm
Perimeter of bottom circle having radius (R) is
=18 cm
Slant height of frustum of cone l=4 cm
Hence,
Radius of top circle r=
2π
6
=
π
3
cm
Radius of bottom circle R=
2π
18
=
π
9
cm
Hight of frustum of cone is
h=
l
2
−(R−r)
2
h=
4
2
−(
π
9
−
π
3
)
2
cm
h=
16−(
π
6
)
2
cm
h=
16−
π
2
36
cm
h=
12.35244
cm
h=3.5146 cm
curved surface area of frustum of cone =π(R+r)l
Step-by-step explanation:
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