To find the length and the height of the box, if the material used is to be a minimum i.e. the AREA of the material is to be a minimum, do the following:
Use the calculator to graph the function and find x when the value of f(x) is minimum.
Once you know x, you can calculate length using the equation. L = 1.5 x
h can be calculated using the equation:
x ^2 * h = 20