how do you tell whether a polynomial is a function or not without using the vertical line test?
Set up a table of values. On one side you will have x's and on another side you will have y's. Let's say on one side, you have different y's and on the the other side, one of the x's repeat. If an x repeats, it's not a function.
A function simply used without the vertical line test - get outta here.
see if the inverse of the function passes the horizontal line test