Question

A rectangular tank with a square​ base, an open​ top, and a volume of 19 comma 65219,652 ft cubedft3 is to be constructed of sheet steel. Find the dimensions of the tank that has the minimum surface area.

Answer 1

34 and 17 feet.

Explanation:

We have that the volume is given by:

V = x * x * y = (x ^ 2) * y

The surface area of the tank would be: x ^ 2 + x * y + x * y + x * y + x * y

SA = x ^ 2 + 4 * x * y

we know that the volume is 19652, replacing it would remain:

19652 = (x ^ 2) * y, we solve for y:

y = 19652 / (x ^ 2)

replacing in SA we are left with:

SA = x ^ 2 + 4 * x * 19652 / (x ^ 2)

SA = x ^ 2 + 70608 / x

we derive and equal 0:

SA´ (x) = 2 * x - 70608 / (x ^ 2) = 0

2 * x = 70608 / (x ^ 2)

x ^ 3 = 39304

x = 34

for and would be:

y = 19652 / (34 ^ 2) = 17

dimensions are 34 and 17 feet.