## Precalculus (6th Edition) Blitzer

The required solution for $x=-1$ and $x=-3$ is $f\left( x \right)=1$.
From the graph one can see that when $f\left( x \right)=1$ (that is, the y-coordinate is 1), the x values are $-1$ and $-3$. Thus, the value of x for which $f\left( x \right)=1$ is $x=-1$ and $x=-3$.