Polynomials that are strictly increasing or strictly decreasing have inverse functions. For example, and are strictly increasing. However, neither nor are one-to-one, and so they do not have an inverse defined for all real .
A polynomial is one-to-one on its intervals of increase and decrease. A restriction of the polynomial is a new function, with one of those intervals as its domain, whose values agree with the values of the polynomial on that interval. Those functions are one-to-one on those intervals and have inverses. For example, the function defined for with values has the inverse function . The function defined for with values has the inverse function .
The graphs of a function and its inverse are symmetric in the line .
This Demonstration plots the graphs of each restricted function (solid curve) and its inverse (dashed curve) in matching colors.