Hey guys, I need to find sin(3 $\displaystyle \pi $ /8)
Alternatively, remember that $\displaystyle \sin{\left(\frac{\pi}{2} - \theta\right)} = \cos{\theta}$.
Can you see that $\displaystyle \frac{\pi}{2} - \frac{\pi}{8} = \frac{3\pi}{8}$?
So that would mean $\displaystyle \sin{\frac{3\pi}{8}} = \cos{\frac{\pi}{8}}$.
And you've been told what that is...