[(m+n)²-(m²-2mn-n²)]÷2n-（n+m）（m-n），其中m=2分之1，n=-1

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原式=(m²+2mn++n²-m²+2mn+n²)÷2n-m²+n²
=(4mn+2n²)÷2n-m²衫空衫迟+n²
=2m+n-m²+n²
=1-1-1/4+1
=3/或塌瞎4

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原式=(m²+2mn++n²-m²+2mn+n²)/2n-m²+n²
=(4mn+2n²)/2n-m²+n²冲或物
=2m+n-m²团升+n²
把m=1/2，n=-1带进去散液
原式=3/4

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