So I have been given a problem to do that involves an incline with an angle . I have been staring this thing down all day and am thinking I have to take the derivative of W. But don't know how to start it.

Any help to get this problem started would be great. Maybe an outline of what I am going to need to do.

Problem:

The largest weightthat can be pulled up a plane inclined at an angle with the horizontal slope by a forceWisF

where is the coefficient of friction. Find so thatis a maximum.W