Horizontal line test

The Horizontal line test is a simple way to see if a function is one-to-one (that is, it has exactly $1$ y-value corresponding with every x-value, or $1$ dependent value for every independent value). If a function passes the Horizontal line test, it has an inverse function. This is because the inverse of a function swaps the domain and range of the original function (the domain of the original function becomes the range of the inverse, and vice versa).

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