Answer
$y=-x$
line passing the pole with an angle of $-\frac{\pi}{4}$ to the polar axis.
See graph.
Work Step by Step
1. Use the formula $tan\theta=\frac{y}{x}$, we have $\theta=-\frac{\pi}{4}\rightarrow \frac{y}{x}=tan(-\frac{\pi}{4})=-1$, or $y=-x$
2. We can identify the above equation as a line passing the pole with an angle of $-\frac{\pi}{4}$ to the polar axis.
3. See graph.