1. Explain, using a unit circle diagram, why cos(180-Θ) = -cos(Θ) 2. My Attempt at a Solution: I have no idea how to begin thinking of this. I don't know any of the obvious details of the question, the only rational thought I can currently form is that cos(Θ) = the x-coordinate of the terminal angle's intersection with a unit circle, however, I don't even know if that's related to the question. I cannot form any simple thoughts regarding this question. I have no idea where to begin, so I'm just wondering if someone here might be able to say something that could point me in the correct direction of an answer. Thanks!