Question

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

Answer 1

`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`:

(Picture source: http://likbez.com/trig/Lesson01/)

or, if you like, is equal to a positive angle of `360°-45°=315°`

(Be careful that for example `cos(-45)=sqrt(2)/2>0`)