An inverse equation, or inverse function, is an equation that reverses another equation. If an equation will give the value of y when providing x, the inverse equation will give the value of x when providing y.
For example, take the following equation: y = 3x - 5. The inverse of this equation is: x = (y + 5) / 3. In the first equation, supplying a value of x = 6 will give y = 13. Then, in the second equation, supplying the value of y = 13 will give x = 6. Therefore, the second equation is the inverse of the first equation.
If an equation has an inverse equation, it is a one-to-one equation, because for every x there is one y, and for every y there is one x. It is possible for there to be no inverse equation for a given equation.