The length of a cedar chest is twice its width. the cost of the lid is four times the cost of the rest of the cedar chest. If the volume is 1440 dm^3, find the dimensions of the box so that the cost is a minimum.
Solve for total Cost:
_____[Lid]____[Base]___[Long Sides]____[Short Sides]___
Find the derivative:
Let c' = 0 to solve for x:
This again is where it get lost, letting the function = 0 is an ongoing problem for me.