rational function: give ex. w/ domain all reals but 3, -1, &

I need help with this problem.

Give an example of a rational function whose domain is the set of real numbers except 3, -1, & & 7.

I don't even know how to start this.

Re: rational functions help

You have to ask yourself, At what points is a function undefined? Then, make one up that is undefined at the points in your problem. Think about concepts like asymptotes, division by zero, etc. How do you make a function so that it is not defined at 3, -1, and 7 because f(x) cannot be computed when x is in {3, -1, 7}? That's how you start.