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Question
If four times the sum of the areas of two circular faces of a cylinder of height 8 cm is equal to twice the curve surface area, then diameter of the cylinder is
Options
4 cm
8 cm
2 cm
6 cm
Solution
Let r be the radius of cylinder.
Area of circular base of cylinder `=pir^2`
The height of cylinder h = 8 cm
The C.S.A. of cylinder`= 2pir xx 8 = 16 pir`
Clearly,
`4 xx (pir^2 + pir^2) = 2 xx (pir)`
`8 pir^2 = 32 pi r`
`8r^2 = 32r`
r = 4cm
The diameter of cylinder
`d = 4 xx 2 = 8 "cm"`
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