A box with a square base and open too must have a volume of 62500 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 3:, the length of one side of the square base. Next, find the derivative, A'(:i:). W) = The critical value is a: = :i The function is until the critical value, and v after, so the critical value corresponds to a local v