已知m的2次方+3mn=5,求5m的2次方-【5m - 知识问答

已知m的2次方+3mn=5,求5m的2次方-【5m的2次方-(2m的2次方-mn)-7mn-5]

2个回答

m^2+3mn=5
5m^2-[5m^2-(2m^2-mn)-7mn-5]
=5m^2-5m^2+(2m^2-mn)+7mn+5
=2m^2-mn+7mn+5
=2m^2+6mn+5
=2(m^2+3mn)+5
=2*5+5
=15

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