You might consider two competing choices (creating a rational equation), a system with multiple ups and downs (polynomial), or an area (quadratic polynomial). Generally, I expect the curve and the general polynomial form describing the shape. Extra points are available for attempting to determine the an... a0terms. At the very least you should consider a system described by a straight line or a constant, the simplest polynomials, in which case full credit will not be given unless the a1and a0 terms are given