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

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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
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

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
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

(x+y+1)(x+y-1)
=(x+y)²-1
=x²+2xy+y²-1

=(x+y)的平方—1的平方
=x的平方+2xy+y的平方—1

x平方+2xy+y平方-1

(x+y+1)(x+y-1)
=[(x+y)+1][(x+y)-1]
=(x+y)²-1
=x²+2xy+y²-1

你的算法错了。你没发现后面中括号里面x的系数变成-1了吗?
原式=[(x+y)+1][(x+y)-1]
  =(x+y)^2-1
   =x^2+2xy+y^2-1