I have the function

$\displaystyle f:[-\pi,\pi] \rightarrow R, f(x) = \sin 3(x+ \frac{\pi}{4})$

and I need to find the endpoints by subbing in $\displaystyle -\pi$ and $\displaystyle \pi$

$\displaystyle f(-\pi) = \sin 3(-\pi + \frac{\pi}{4})$

$\displaystyle = \sin 3(\pi+\frac{\pi}{4})$

$\displaystyle = \sin (3\pi+\frac{3\pi}{4})$

$\displaystyle = \sin (2\pi+\frac{7\pi}{4})$

$\displaystyle = \sin (\frac{7\pi}{4})$

Is this right so far? If so, what do I do next?

Thanks.