M-2N=(3x²+2x-1)-2(-x²-2+3x)=3x²+2x-1+2x²+4-6x=5x²-4x+3代入法：M-2N=(3x²+2x-1)-2(-x²-2+3x)=(3×1²+2×1-1)-2(-1²-2+3×1)=4-2×0=4化简法：M-2N=5x²-4x+3=5...对不起，我打错了。是当x＝-1时，那等于多少呢？代入法：M-2N=(3x²+2x-1)-2(-x²-2+3x)=[3×(-1)²+2×(-1)-1]-2[-(-1)²-2+3×-(1)]=0-2×(-6)=12 化简法：M-2N=5x²-4x+3=5×(-1)²-4×(-1)+3=12不是啊，我说的代入法是直接用数字。M-2N=(3x²+2x-1)-2(-x²-2+3x)=[3×(-1)²+2×(-1)-1]-2[-(-1)²-2+3×-(1)]=0-2×(-6)=12这个就是直接代入数字