∫ln(1＋x^2)dx=x*ln(1＋x^2)-∫x*dln(1＋x^2)=x*ln(1＋x^2)-∫2x^2/(1+x^2)dx
=x*ln(1＋x^2)-2∫[1-1/(1+x^2)]dx
=x*ln(1＋x^2)-2x+arctanx+c