A box with a square base and open top must have a volume of 157216 cm3. We wish to find the dimensions of the box that minimize the amount of material used. First, find a formula for the surface area of the box in terms of only x, the length of one side of the square base.
[Hint: use the volume formula to express the height of the box in terms of x.]
Simplify your formula as much as possible.
A(x)=
Next, find the derivative A′(x).
A'(x)=
Now, calculate when the derivative equals zero, that is, when A′(x)=0. [Hint: multiply both sides by x2.]
A'(x)=0 when x=
We next have to make sure that this value of x gives a minimum value for the surface area. Let's use the second derivative test. Find A"(x).
A"(x)=
Evaluate A"(x) at the x-value you gave above.