已知A÷x²-y²/x²+4xy+4y²=x+2y/x+y,当x=2,y=1时,

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已知A÷x²-y²/x²+4xy+4y²=x+2y/x+y,当x=2,y=1时,求A的值

你用括号分一下吧~
是如下所示吗?
A÷（(x²-y²)/(x²+4xy+4y²)）=(x+2y)/(x+y)
A =(x+2y)/(x+y) * (x²-y²)/(x²+4xy+4y²)
=(x+2y)(x+y)(x-y) / (x+y)(x+2y)(x+2y)
=(x-y)/(x+2y) ----(x+y)*(x+2y)≠0
当x=2,y=1时,(x+y)*(x+2y)≠0
所以A = (2-1) / (2+1*2) = 1/4

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