Originally Posted by

**D. Martin** I do not know why cos pi is equivalent to -1. Generally, on the unit circle I've been learning of since a day ago, it shows all the fractions of pi arranged around the circle. Each pi fraction extends from the centre of the coordinate plane and forms a right angle triangle. With most of the right triangles I have a sort of intuitive grasp of them. But I don't see any trangle that can be constructed on the unit circle that would make sense of cos pi = -1.

I mean, with any triangle wouldn't the hypotunse being some value like the root of 3 prevent cos pi from being -1? I mean, -1 over 3 pi or something would make sense. But just -1?

I'm sorry about not be able to provide a more detailed attempted answer. I'm also sorry for the inelegance of this post. I just really do not have a good grasp of the unit circle. I know my thoughts are probably quite far off the correct answer.