Inverse Functions

You already know how a function turns an input into an output. An inverse function does the reverse: it takes the output back to the input it came from. Think of it as the undo button for a function. If one machine doubles a number and adds three, the inverse machine must subtract three and then halve, exactly reversing each step in the opposite order.

But not every function can be undone. In this lesson you will learn the crucial test of whether an inverse even exists, why a function must be one-one to have one, and the reliable swap-and-rearrange method for finding the inverse. These ideas sit at the heart of the Functions section and reward careful, tidy algebra.