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已知m+n=3,mn=-2,求多项式2(mn+m)-[-(3n-mn)-m]+mn的值(先化简,再求值)
人气:135 ℃ 时间:2019-12-09 01:37:05
解答
2(mn+m)-[-(3n-mn)-m]+mn
  =2mn+2m+3n-mn+m+mn
  =2mn+3m+2n
  =2mn+3(m+n)
  ∵m+n=3,mn=-2
  ∴2(mn+m)-[-(3n-mn)-m]+mn
  =2mn+3(m+n)
  =2×(-2)+3×3
  =-4+9
  =5
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