# Math Help - Standard Domain Restrictions on Cos(x)?

1. ## Standard Domain Restrictions on Cos(x)?

What is the standard domain restriction we put onto f(x)=cos(x) so that it is a one-to-one function?
I am having the toughest time trying to understand what the question is asking in the first place. I am either assuming its one period of cos(x), or the upper/lower half of a circle. Any ideas?

2. Originally Posted by KinXen
I am having the toughest time trying to understand what the question is asking in the first place. I am either assuming its one period of cos(x), or the upper/lower half of a circle. Any ideas?
For a function to be 1 to 1 there can only be one y for every x. As indicated on the graph below the simplest thing to do is to restrict the domain to $(0, \pi )$.

-Dan