Chapter 1 - Section 1.6 - Inverse Functions and Logarithms - Exercises - Page 48: 7

Not one-to-one.

According to the Horizontal Line Test, a function is one-to-one if and only if every horizontal line intersects the graph at at most one point. Here, the test fails at the horizontal line of $y=3$, so the function is not one-to-one.