Chapter 4 - Exponential and Logarithmic Functions - Section 4.2 One-to-One Functions; Inverse Functions - 4.2 Assess Your Understanding - Page 291: 22

The given graph fails the Horizontal Line Test, so it is not a one-to-one function.

The Horizontal Line Test states that when all the horizontal lines intersect the function graph at no more than one point, then the function is said to be one-to-one. Since the graph is symmetric about the $y-axis$, it fails the Horizontal Line Test, so it is not a one-to-one function.