∫(1＋x^2－1)arctanx/(1+x^2)dx=∫(1＋x^2)arctanx/(1+x^2)dx-∫arctanx/(1+x^2)dx=∫arctanxdx-∫arctanx/(1+x^2)dx=xarctanx-∫x/(1+x^2)dx-∫arctanxd(arctanx)=xarctanx-1/2∫1/(1+x^2)d(1+x^2)-1/2(arctanx)^2...