全部展开就是了
∫(1-X)(1-2X)(1-3X)dx
=∫(-6x^3+11x^2-6x+1)
=-6*x^4/4+11*x^3/3-6*x^2/2+x+C
=(-3/2)x^4+(11/3)x^3+3x^2+x +C