Intermediate Algebra (6th Edition)

We know that a function is one-to-one if each x-value of the function corresponds to only one y-value and each y-value corresponds to only one x-value. The given function is $y=-x+2$, which is a line with a slope of -1 that crosses the y-axis at $x=2$. This function is one-to-one, because each x-value of the function corresponds to only one y-value, and vice versa. In general, all lines besides horizontal and vertical lines will be one-to-one functions.