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 (a) 4 cm     (b) 8 cm     (c) 2 cm      (d) 6 cm

Explanation

circular base area of cylinder ` =pi r^{2}`


cylinder height `h=8 cm`


The Curved Surface Area of cylinder `=2 pi r times 8=16 pi r`


`4 times(pi r^{2}+pi r^{2}) =2 times(pi r) `

`
8 pi r^{2} =32 pi r`

`
8 r^{2} =32 r `

`
r =4 cm`



...