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

पर्याय

• 4 cm

• 8 cm

• 2 cm

• 6 cm

Answer 1

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"`