# What is the value of sin -45^@?

sin(-45°)=-sqrt(2)/2
This is the same as 45° but starting clockwise from the $x$ axis giving you a negative value of the $\sin$:
or, if you like, is equal to a positive angle of 360°-45°=315°
(Be careful that for example $\cos \left(- 45\right) = \frac{\sqrt{2}}{2} > 0$)