18. Let *f*(*x*) = 3*x* + 4. Find *f* ^{-1}(*x*). Graph both *f* and *f* ^{-1} in the same coordinate system.

Let *y* = 3*x* + 4 and solve for *x*

*y* - 4 = 3*x*

So

thus

For the graph, *f*(*x*) has a slope of 3 and a *y-*intercept of 4. *f* ^{-1}(*x*) has a slope of 1/3 and a *y*-intercept of 4/3.

Not that the graph of *f*^{-1}(*x*) is the reflection of the graph of *f*(*x*) about the line *y* = *x*.