用平方差计算(x+y+1)(x+y-1),
用平方差计算(x+y+1)(x+y-1),
原式=[y+(x-1)][y-(x-1)]
=y²-(x-1)²
=y²-x²+2x-1
原式=[y+(x-1)][y-(x-1)]
=y²-(x-1)²
=y²-x²+2x-1
数学人气：675 ℃时间：2020-04-04 22:59:38
优质解答
X^2+Xy-X+Xy+y^2-y+x+y-1 化简得x^2+2xy+y^2+y-1再化简得（x+y）^2+y+1
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