#41 Function Plotter - Cusps

[Darin Gillis]

The 1-D function plotter does not handle cusps
correctly. I suspect that the problem comes from f'(x)
not being defined at the cusp point--and we are not
handling that situation correctly.

The specific function that caused trouble is:

f(x) = x^(5/3) + 5*x^(2/3)

only the right half of the function gets plotted; while
there is a downwards-pointing parabola on the left that
should be displayed (max at x=-2)