Trig
posted by Meg .
The postal service places a limit of 84 inches on the combined lenght and girth (distance around) of a package to be sen parcel post. What Dimensions of a rectangular box with square crosssection will contain the largest volume that can be mailed?

4x+y = 84, so
y = 844x
v = x^2 y = x^2(844x) = 84x^2  4x^3
dv/dx = 168x  12x^2
= 12x(14x)
dv/dx=0 when x=14
so the box is 14 x 14 x 28