Because 135=90+45, 135 is an angle in the second quadrant which makes an angle of 45 with the positive y-axis.
We can determine the point on the unit circle which corresponds to 135 by introducing an auxiliary triangle and calculating its edges using trigonometry.
oppositeadjacent=1sin45=12=1cos45=12
The coordinates of the point are (−1212) and this shows that cos135=−12.
=90
sin45
2=1
1