Answer
The horizontal line test determines if a function is a one-to-one function. If a graph passes the test, that means the function has an inverse function because for each $x$-value, there is only one $y$-value and the relation $f^{-1}$ is a function. If the horizontal line passes through the graph more than once, the function lacks an inverse function.
Work Step by Step
The horizontal line test is performed by drawing a horizontal line through a graph to see if it touches more than one point on the graph.
