I donot remember how to convert radians to dregrees and back again, also simplfying these answers would be great. I.E.: -23pi/3 but the answer must be between 0 and 2pi
$\displaystyle radians=degrees\cdot\frac{\pi}{180}$
For the second half of your question:
You must find the reference angle. This means to find what quadrant the angle lies in, and then determine whatever you need by referencing the x-axis - whether it be the sin, cos tan, etc...
EG
$\displaystyle \frac{9\pi}{4}$ has a refernce angle of $\displaystyle \frac{\pi}{4}$. The point is that no matter how many times the angle goes around the circle, all of the trig rules apply as if it is the first time. This is called periodicity.