# Math Help - restriction

1. ## restriction

Give a restriction on the function y=f(x)=ax2+bx+c so that its inverse f-1 exists, is either strictly increasing throughout its domain, or strictly decreasing, and so that no larger domain possesses these properties.

2. ## Re: restriction

Originally Posted by franios
Give a restriction on the function y=f(x)=ax2+bx+c so that its inverse f-1 exists, is either strictly increasing throughout its domain, or strictly decreasing, and so that no larger domain possesses these properties.
Inverse functions only exist when the original function is one-to-one. Since it's a quadratic, it will be one-to-one (and in this case, strictly increasing/decreasing) from the turning point on in either direction (but not both).