要用分部积分法
∫x^2*arctan(7x)dx
=(x^3/3)*arctan(7x)-∫(x^3/3)*7/(49x^2+1)
=(x^3/3)*arctan(7x)-7/6∫x^2/(49x^2+1)d(x^2)
=(x^3/3)*arctan(7x)-(x^2/42-(1/2048)*ln|x^2+1/49|)
=(x^3/3)*arctan(7x)-x^2/42+(1/2048)*ln|x^2+1/49|+C
要用分部积分法
∫x^2*arctan(7x)dx
=(x^3/3)*arctan(7x)-∫(x^3/3)*7/(49x^2+1)
=(x^3/3)*arctan(7x)-7/6∫x^2/(49x^2+1)d(x^2)
=(x^3/3)*arctan(7x)-(x^2/42-(1/2048)*ln|x^2+1/49|)
=(x^3/3)*arctan(7x)-x^2/42+(1/2048)*ln|x^2+1/49|+C