因式分解：X^3+3X^2
因式分解： X^3+3X^2-5X+1
X^3+3X^2-5X+1 =(x^3+2x^2-3x)+(x^2-2x+1) =x(x+3)(x-1)+(x-1)^2 =(x-1)(x^2+4x-1)