Q. 20 4.1( 47 Votes )

Show that the right circular cylinder of given surface and maximum volume is such that its height is equal to the diameter of the base.

Answer :

Let r be the radius and h be the height of the cylinder.

Then, the surface area (S) of the cylinder is given by:

S = 2πr2 + 2πrh


Let V be the volume of the cylinder. Then

V = πr2h



So, when then <0

Then, by second derivative test, the volume is the maximum when

Now, when . then h =

Therefore, the volume is the maximum when the height is the twice the radius or height is equal to diameter.

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Show that the maximum value of is

RS Aggarwal - Mathematics