Please help me with my algebruh :) Spelt it like that on purpose.. Here is the link to the question I asked before. It has the screenshots and whatnot!

Trent wants to buy 2 packs of trading cards for 3 dollars each. the trading card packs that trent normally buys tend to come in packs of 6, 10, 12, or 15 cards. after selecting 2 packs, trent found that the first pack of cards cost 25 cents per card, and the second pack cost 30 cents per card. trent uses this information to write the equations below in order to compare c, the number of cards in each pack.

Sketch one cycle if the cosine function y=2cos2theta

We just started the introduction into circles and i have no idea how to do this.