Checking Validity of Functions and Inverse Functions

Sometimes it can be hard to tell whether or not a graph or equation is a valid function or not. Here are some simple steps to checking this:

Horizontal line test: If a straight line can be drawn horizontally that crosses the graph in two places, then this function is called a many to one function. This is only true if a values of x are plotted. However, when finding the inverse of this function, the graph will be reflected in y=x and will no longer abide by the Horizontal line test, but the Vertical line test.

Vertical Line test: If a straight, vertical line can be drawn that crosses the graph in two places, then this is 'one to many' which is not a function. 

1) Vertical line test true = not a function.

2) Horizontal line test true = many to one function

    Horizontal line test true = inverse will not be a function.