Answer
$\dfrac{3\pi}{4}, \dfrac{7\pi}{4}$
Work Step by Step
Since $\tan{\theta} = \dfrac{\cos{\theta}}{\sin{\theta}}$
As $\tan{\theta} = -1$, we search figure 22 for points where $\cos{\theta} = -\sin{\theta}$
The two angles on the unit circle where $\cos{\theta} = -\sin{\theta}$ are $\dfrac{3\pi}{4}$ and $\dfrac{7\pi}{4}$
$\theta = \dfrac{3\pi}{4}, \dfrac{7\pi}{4}$
