Sx^2dx/(1+x^2) = S(x^2+1)dx/(1+x^2) - Sdx/(1+x^2) = Sdx - arctan(x) = x - arctan(x) + C,
其中C为任意常数。
S_{x:a->b}x^2dx/(1+x^2) = [x - arctan(x)]|_{x:a->b} = [b - arctan(b)] - [a - arctan(a)] = b - a + arctan(a ) - arctan(b).
(1) 化简积分
(2) 利用公式求解
∫x^2/(1+x^2)dx
=∫1-1/(1+x^2)dx
=x-arctanx+C