The angle of -315 degree means angle of 315 degree in clockwise direction from the positive x-axis.
The angle -315 degree means that angle lies in first quadrant as,
So measure of reference angle is,
[tex]360-315=45[/tex]
Reference angle in radians is,
[tex]45\cdot\frac{\pi}{180}=\frac{\pi}{4}[/tex]
So reference angle of -315 degree in radians is,
[tex]\frac{\pi}{4}\text{ radians}[/tex]
