A/5/9.4/-7 B/5 2/3.9/7-17/7.2/3 C/-1,4.15/49 -(80%+2/3):11/5 BÀI 2 A/x+1/3=-1/5 b/-3/4:x=1/2

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1. Đáp án:

   $\begin{array}{l}
   a)\dfrac{5}{9}.\dfrac{4}{{ – 7}} = \dfrac{{ – 20}}{{63}}\\
   b)\dfrac{2}{3}.\dfrac{9}{7} – \dfrac{{17}}{7}.\dfrac{2}{3}\\
    = \dfrac{2}{3}.\left( {\dfrac{9}{7} – \dfrac{{17}}{7}} \right)\\
    = \dfrac{2}{3}.\dfrac{{ – 8}}{7}\\
    = \dfrac{{ – 16}}{{21}}\\
   c) – 1,4.\dfrac{{15}}{{49}} – \left( {80\%  + \dfrac{2}{3}} \right):\dfrac{{11}}{5}\\
    = \dfrac{{ – 14}}{{10}}.\dfrac{{15}}{{49}} – \left( {\dfrac{{80}}{{100}} + \dfrac{2}{3}} \right).\dfrac{5}{{11}}\\
    = \dfrac{{ – 7}}{5}.\dfrac{{15}}{{49}} – \left( {\dfrac{4}{5} + \dfrac{2}{3}} \right).\dfrac{5}{{11}}\\
    = \dfrac{{ – 3}}{7} – \left( {\dfrac{{12 + 10}}{{5.3}}} \right).\dfrac{5}{{11}}\\
    = \dfrac{{ – 3}}{7} – \dfrac{{22}}{3}.\dfrac{1}{{11}}\\
    = \dfrac{{ – 3}}{7} – \dfrac{2}{3}\\
    = \dfrac{{ – 23}}{{21}}\\
   2)\\
   a)\dfrac{{x + 1}}{3} =  – \dfrac{1}{5}\\
    \Rightarrow x + 1 =  – \dfrac{1}{5}.3 =  – \dfrac{3}{5}\\
    \Rightarrow x =  – \dfrac{3}{5} – 1\\
    \Rightarrow x = \dfrac{{ – 3 – 5}}{5} = \dfrac{{ – 8}}{5}\\
   b) – \dfrac{3}{4}:x = \dfrac{1}{2}\\
    \Rightarrow x =  – \dfrac{3}{4}:\dfrac{1}{2}\\
    \Rightarrow x =  – \dfrac{3}{4}.2\\
    \Rightarrow x =  – \dfrac{3}{2}
   \end{array}$

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