x^3一3x十2
=x^3-x-2x+2
=x(x^2-1)-2(x-1)
=x(x+1)(x-1)-2(x-1)
=(x-1){x(x+1)-2}
=(x-1)(x^2+x-2)
=(x-1)(x-1)(x+2)
=(x-1)^2 (x+2)