tìm x thuộc z , 5/17+-4/19+-20/21+12/17+-11/31

27/10/2021 Bởi Alaia

0 bình luận về “tìm x thuộc z , 5/17+-4/19+-20/21+12/17+-11/31<x/9< hoặc bằng -3/7+7/15+4/-7+8/15+2/3”

1. Đáp án: $x\in\{-4,-3,-2,-1,0,1,2,3,4,5,6\}$

   Giải thích các bước giải:

   Ta có:

   $\dfrac{5}{17}+\dfrac{-4}{19}+\dfrac{-20}{21}+\dfrac{12}{17}+\dfrac{-11}{31}<\dfrac{x}{9}\le \dfrac{-3}{7}+\dfrac7{15}+\dfrac{4}{-7}+\dfrac8{15}+\dfrac23$

   $\to (\dfrac{5}{17}+\dfrac{12}{17})+\dfrac{-4}{19}+\dfrac{-20}{21}+\dfrac{-11}{31}<\dfrac{x}{9}\le (\dfrac{-3}{7}+\dfrac4{-7})+(\dfrac7{15}+\dfrac8{15})+\dfrac23$

   $\to 1+\dfrac{-4}{19}+\dfrac{-20}{21}+\dfrac{-11}{31}<\dfrac{x}{9}\le (\dfrac{-3}{7}-\dfrac4{7})+1+\dfrac23$

   $\to \dfrac{12369}{12369}-\dfrac{2604}{12369}-\dfrac{11780}{12369}-\dfrac{4389}{12369}<\dfrac{x}{9}\le -1+1+\dfrac23$

   $\to -\dfrac{6404}{12369}<\dfrac{x}{9}\le \dfrac23$

   $\to -\dfrac{19212}{4123}<x\le \:6$

   $\to -4\le x\le 6$ vì $x\in Z$

   $\to x\in\{-4,-3,-2,-1,0,1,2,3,4,5,6\}$

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