1.Tìm x, biết a,11/13 – ( 5/42 – x ) = – (15/28 – 11/13 ) b,x + 1/3 =2/5 – ( -1/3) c,-5/8 – x = -3/20 – (-1/6) d,x-(-1/4)=-5/6+1/8 e,-2/3x=4/15 g, x :

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1. Đáp án:

   a, $\dfrac{-5}{28}$

   b, $\dfrac{2}{5}$ 

   c, $\dfrac{-77}{120}$

   d, $\dfrac{-23}{24}$ 

   e, $\dfrac{-2}{5}$ 

   g, $\dfrac{-176}{405}$ 

   Giải thích các bước giải:

   a,

   $\dfrac{11}{13}-\left ( \dfrac{5}{42}-x \right )= -\left ( \dfrac{15}{28}-\dfrac{11}{13} \right )$ 
   $= \dfrac{-15}{28}+\dfrac{11}{13}$
   $\Rightarrow \dfrac{5}{42}-x= \dfrac{15}{28}\Rightarrow x= \dfrac{5}{42}-\dfrac{15}{28}= \dfrac{-5}{28}$

   b, 

   $x+\dfrac{1}{3}= \dfrac{2}{5}-\left ( \dfrac{-1}{3} \right )= \dfrac{2}{5}+\dfrac{1}{3}$
   $\Rightarrow x= \dfrac{2}{5}$ 

   c,

   $\dfrac{-5}{8}-x= \dfrac{-3}{20}-\dfrac{-1}{6}= \dfrac{-3}{20}+\dfrac{1}{6}= \dfrac{1}{62}$
   $\Rightarrow x= \dfrac{-77}{120}$ 

   d, 

   $x-\left ( -\dfrac{1}{4} \right )= \dfrac{-5}{6}+\dfrac{1}{8}$
   $\Rightarrow x= \dfrac{-5}{6}+\dfrac{1}{8}-\dfrac{1}{4}= \dfrac{-23}{24}$ 

   e,

   $\dfrac{-2x}{3}= \dfrac{4}{15}$
   $\Rightarrow x= \dfrac{4}{15}:\dfrac{-2}{3}= \dfrac{-2}{5}$ 

   g,

   $x:\dfrac{22}{15}= \dfrac{-8}{27}$
   $\Rightarrow x= \dfrac{-8}{27}.\dfrac{22}{15}= \dfrac{-176}{405}$

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