①2x^2＋xy－y^2－4x＋5y－6
问题描述：
①2x^2＋xy－y^2－4x＋5y－6
②x^2＋4xy－4y^2,我算出来=﹙x＋2y＋2√2·y﹚﹙x＋2y－2√2·y﹚
③x^2＋2x－1=(x＋1＋√2)(x＋1－√2)对不对?
答
2x^2+xy-y^2-4x+5y-6=(2x-y)(x+y)-4x+5y-6=(2x-y)(x+y)+(2x+2y)-6x+3y-6=(2x-y)(x+y)+2(x+y)-6x+3y-6=(x+y)(2x-y+2)-3(2x-y+2)=(x+y-3)(2x-y+2)对的x^2+4xy-4y^2=x^2+4xy+4y^2-8y^2=(X+2Y)^2-8y^2=(X+2Y-2√2Y)(X+2Y...