∫x^2 * arctanxdx=1/3×∫arctanxd(x^3)=1/3×x^3×arctanx-1/3×∫x^3/(1+x^2)=1/3×x^3×arctanx-1/3×∫(x^3+x-x)/(1+x^2)=1/3×x^3×arctanx-1/3×∫xdx+1/3×∫x/(1+x^2)=1/3×x^3×arctanx-1/6×x^2+1/6×ln(1+x^2)+C
到底是∫x^3/(1+x^2)dx还是∫x^2/(1+x^3)dx