已知x+y=-1,xy=6求（6xy+7y)+{8 - 知识问答

已知x+y=-1,xy=6求（6xy+7y)+{8x-(5xy-y+6)}

3个回答

因为x+y=-1所以x=-1-y,又因为xy=6,
（6xy+7y)+{8x-(5xy-y+6)}
=6xy+7y+8x-(5xy-y+6)
=6xy+7y+8x-5xy+y-6
=xy+8y+8x-6
把x=-1-y,xy=6代入xy+8y+8x-6
=6+8y+8(-1-y)-6
=6+8y-8-8y-6
=6-8-6
=-8

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