(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
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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