A-2B=3X^2-2X+1-2(-2X+X^2-2)
=3X^2-2X+1-2X^2+4X+4
=X^2+2X+5
由B=-2X+X^2-2可得:X^2=-2X-2
带入:A-2B=-2X-2+2X+5=3