>>531
(2)
2∫x^2/(1+x^2)^2 dx
= ∫x*{2x/(1+x^2)^2}dx (ここで部分積分をやる)
= x*{-1/(1+x^2)} - ∫{-1/(1+x^2)}dx
= -x/(1+x^2) + ∫1/(1+x^2) dx
= -x/(1+x^2) + arctan(x) + C