Answer
$-\frac{3\pi}{4}$ radians
Work Step by Step
To convert from degrees to radians, the measurement in degrees must be multiplied by $\frac{\pi}{180}$.
Therefore
$-135°= -135° \times \frac{\pi}{180}$
$=-\frac{135\pi}{180}$
$=-\frac{3\pi}{4}$ radians