1. The problem statement, all variables and given/known data 3. The attempt at a solution I'm having a tough time understanding this step. I understand that the integral of 1/sqrt(a^2-x^2) = arcsin(u/a) + C But sqrt(4-x^2) does not have a 1 in the numerator. It looks like they're using u substitution, if so, then why is it + 4 arcsin rather than times 4arcsin. I also don't understand where the 4 comes from.