Your answer to a) is right. I presume your answer to b) is right also (it's just a matter of plotting points after all.)

For c) what we want to do is look at how the graph of looks on the domain 180 - 360 degrees vs. the domain 0 to 180 degrees.

The first thing you can do is simply take an educated guess: you know what the cosine function looks like so you ought to be able to extend the graph. Otherwise, plot the points and see what it looks like. (I've graphed the domain 0 - 360 degrees below. In the graph the argument of the cosine function is in radians, but you can figure it out from there.)

The vertical blue dotted line is the break between 0 - 180 degrees and 180 - 360 degrees. What do you need to do to the graph from 0 - 180 degrees to get the graph from 180 - 360 degrees?

-Dan