I am trying to find out the angles of a triangle based on the lengths of the sides. I found this:
Let △ABC have sides a, b, and c.
We are using the usual convention that the length of the side
opposite vertex A is called a, and so on.
Let θ=∠C. Then the Cosine Law says that
c^2 = a^2 + b^2 − 2ab cosθ`
So how do you reverse this to get θ?