(x-2y+2)²-(x-2y+2)(x+2y+2)不要用巧算 用死算怎么不一样 死算是-4xy-8y 我用完
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(x-2y+2)²-(x-2y+2)(x+2y+2)不要用巧算 用死算怎么不一样 死算是-4xy-8y 我用完全平方公式做的
![(x-2y+2)²-(x-2y+2)(x+2y+2)不要用巧算 用死算怎么不一样 死算是-4xy-8y 我用完](/uploads/image/z/8868698-26-8.jpg?t=%EF%BC%88x-2y%2B2%EF%BC%89%26%23178%3B-%28x-2y%2B2%29%28x%2B2y%2B2%29%E4%B8%8D%E8%A6%81%E7%94%A8%E5%B7%A7%E7%AE%97+%E7%94%A8%E6%AD%BB%E7%AE%97%E6%80%8E%E4%B9%88%E4%B8%8D%E4%B8%80%E6%A0%B7+%E6%AD%BB%E7%AE%97%E6%98%AF-4xy-8y+%E6%88%91%E7%94%A8%E5%AE%8C)
正确答案是8y^2-4xy-8y
死算法:(x-2y+2)²-(x-2y+2)(x+2y+2)
=(x²-4xy+4y²+4x-8y+4)-(x²+4x+4-4y²)
=8y²-4xy-8y
巧算法:设t=x+2
(x-2y+2)²-(x-2y+2)(x+2y+2)
=(t-2y)²-(t-2y)(t+2y)
=(t-2y)(t-2y-t-2y)
=(t-2y)×(-4y)
=-4yt+8y²
=8y²-4xy-8y
死算法:(x-2y+2)²-(x-2y+2)(x+2y+2)
=(x²-4xy+4y²+4x-8y+4)-(x²+4x+4-4y²)
=8y²-4xy-8y
巧算法:设t=x+2
(x-2y+2)²-(x-2y+2)(x+2y+2)
=(t-2y)²-(t-2y)(t+2y)
=(t-2y)(t-2y-t-2y)
=(t-2y)×(-4y)
=-4yt+8y²
=8y²-4xy-8y
(x-2y+2)²-(x-2y+2)(x+2y+2)不要用巧算 用死算怎么不一样 死算是-4xy-8y 我用完
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