Heya!
Ok, here is the exercise:
Thanks in Advance!
Oh! Thanks!
But can you please explain one more thing...
´
How did u get $\displaystyle \cos{\beta} = \cos{\pi}\cos{\alpha} + \sin{\pi}\sin{\alpha}$ from $\displaystyle \cos{\beta} = \cos(\pi - \alpha)$
and $\displaystyle \cos{\beta} = (-1)\cos{\alpha} + (0)\sin{\alpha} = -\cos{\alpha}$
from $\displaystyle \cos{\beta} = \cos{\pi}\cos{\alpha} + \sin{\pi}\sin{\alpha}$