答：
x立方-2x平方+4x+7
=x^3-2x^2+4x+7
=(x^3+1)-2(x^2-2x-3)
=(x+1)(x^2-x+1)-2(x+1)(x-3)
=(x+1)(x^2-x+1-2x+6)
=(x+1)(x^2-3x+7)