Equation: The operator types in an equation in the
form Ax^4+BX^3+Cx^2+Dx+E the equation is drawn.
The operator can then, through a menu, ask for the
solution(s) for x, a value for y for a value of x and the       
line for dy/dx for a value of x for which the slope
is given and the line drawn. Values for A-D can be zero.