The question asks for the area bounded by y=4 and 4/(1+x^2) from x=-1 to x=1.

I used definition integral to do this question and get (4x - 4*arctan(x)) from x=-1 to x=1.

However, when I plug in the numbers, I don't know which value to use for arctan(-1). If I use arctan(-1) = 3 pi/4, I would get an answer from the answer key. (The answer key says arctan(-1) = -pi/4.

How do I know which value I should use?

Please help me! Thanks!