Originally Posted by

**Quacky** $\displaystyle \sin\theta=\frac{-1}{\sqrt{2}}$

Taking $\displaystyle \theta=-45$ and knowing that $\displaystyle \cos(-x)=\cos(x)$ makes this fairly straightforward once you've used the unit circle.

For $\displaystyle \cos\theta =\frac{-24}{25}$, consider a $\displaystyle 7$,$\displaystyle 24$,$\displaystyle 25$ right triangle and the property $\displaystyle -\sin\theta=\sin{(-\theta)}$ combined with the one mentioned previously. I think this is all you should need to get a solution.