tim x a)x=1/5+2/11 b)x=1/13+-13/26 c)x=1/12+3/4 +-2/9 d) x/5=5/6+-19/30

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1. a) x = 1/5 + 2/11

       x = 11/55 + 10/55

       x = (11 + 10) / 55

       x = 21/55

   Vậy x = 21/55

   b) x = 1/13 + (-13/26)

       x = 1/13 – 13/26

       x = 2/26 – 13/26

       x = (2 – 13) / 26

       x = -11/26

   c) x = 1/12 + 3/4 + (-2/9)

       x = 1/12 + 3/4 – 2/9

       x = (1/12 + 3/4) – 2/9

       x = (1/12 + 9/12) – 2/9

       x = [(1 + 9) / 12] – 2/9

       x = 10/12 – 2/9

       x = 5/6 – 2/9

       x = 11/18

   Vậy x = 11/18

   d) x/5 = 5/6 + (-19/30)

       x/5 = 5/6 – 19/30

       x/5 = 25/30 – 19/30

       x/5 = 6/30

       x/5 = 1/5

           x = 1

   Vậy x = 1

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2. Đáp án:

    

   Giải thích các bước giải:

   a) x=$\frac{1}{5}$ +$\frac{2}{11}

   ⇔x=$\frac{11}{55}+ $\frac{10}{55}

   ⇒x=$\frac{21}{55}

   b) x=$\frac{1}{13}-$\frac{13}{26}

       ⇔x=$\frac{2}{26}-$\frac{13}{26}

       ⇒x=$\frac{-11}{26}

   c) x=$\frac{1}{12}+$\frac{3}{4}-$\frac{2}{9}

     ⇔ x=$\frac{1}{12}+$\frac{9}{12}-$\frac{2}{9}

     ⇔ x= $\frac{5}{6}-$\frac{2}{9}

     ⇒ x=$\frac{11}{18}

   d) $\frac{x}{5}=$\frac{5}{6}-$\frac{19}{30}

       ⇔ $\frac{x}{5}= $\frac{25}{30}-$\frac{19}{30}

       ⇔$\frac{x}{5}=$\frac{1}{5}

       ⇔5x=5

   => x=1

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