Find the dimensions of a cylinder of volume 17 m3 of minimal cost if the top and bottom are made of material that costs twice as much as the material for the side.

The answer is below

Step-by-step explanation:

The volume of the cylinder with radius (r) and height (h) is given as:

Volume = πr²h

17 = πr²h

h = 17 / πr²

Let k represent the cost of the side and 2k the cost of the bottom.

The area of the side = 2πrh, hence the cost of the side = k(2πrh)

The area of the top and bottom = 2πr², hence the cost of the top and bottom = 2k(2πr²)

The total cost (T) = cost of side + cost of the top and bottom

T = k(2πrh) + 2k(2πr²)

T = 2kπ(rh + 2r²)

Put h = 17/πr²

T = 2kπ (r×17/πr² + 2r²)

T = 2kπ(17/πr + 2r²)

The minimal cost is at dT/dr = 0

the answer will be the last one