Answer
$\frac{\sqrt 2}{2}$, $-\frac{1}{2}$
Work Step by Step
Step 1. $t=\frac{\pi}{4}$ gives a point $(\frac{\sqrt 2}{2},\frac{\sqrt 2}{2})$ on a unit circle, thus $sin(\frac{\pi}{4})=\frac{\sqrt 2}{2}$
Step 2. $t=\frac{8\pi}{3}=2\pi+\frac{2\pi}{3}$ gives a point $(-\frac{1}{2},\frac{\sqrt 2}{2})$ on a unit circle, thus $cos(\frac{8\pi}{3})=-\frac{1}{2}$
