8a. Tìm x a) 2/5 . x + 1/3 = 1/5 b) 4/9 – 5/3 . x = -2 c) 1/5 + 5/3 : x = 1/2 d) 5/7 : x – 3 = -2/7

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1. Đáp án:

    a ) Ta có :

   $\frac{2}{5}$ .x + $\frac{1}{3}$ = $\frac{1}{5}$

   =>  $\frac{2}{5}$ .x = $\frac{1}{5}$ – $\frac{1}{3}$

   => $\frac{2}{5}$ .x = $\frac{-2}{15}$

   => x = $\frac{-2}{15}$ : $\frac{2}{5}$

   => x = $\frac{-1}{3}$

   Vậy x = $\frac{-1}{3}$

   b ) Ta có :

   $\frac{4}{9}$ – $\frac{5}{3}$ . x = – 2

   => $\frac{5}{3}$ . x  = – 2 – $\frac{4}{9}$

   => $\frac{5}{3}$ . x = $\frac{-22}{9}$

   => x = $\frac{-22}{9}$ : $\frac{5}{3}$

   => x = $\frac{-22}{15}$

   Vậy x = $\frac{-22}{15}$

   c ) Ta có :

   $\frac{1}{5}$  + $\frac{5}{3}$ : x = $\frac{1}{2}$

   => $\frac{5}{3}$ : x = $\frac{1}{2}$ – $\frac{1}{5}$

   => $\frac{5}{3}$ : x = $\frac{3}{10}$ 

   => x = $\frac{5}{3}$ : $\frac{3}{10}$

   => x = $\frac{50}{9}$

   Vậy x = $\frac{50}{9}$

   d ) Ta có :

   $\frac{5}{7}$ : x  – 3 = $\frac{-2}{7}$

   => $\frac{5}{7}$ : x = 3 + $\frac{-2}{7}$

   => $\frac{5}{7}$ : x  = $\frac{19}{7}$

   =>  x = $\frac{5}{7}$ : $\frac{19}{7}$

   => x = $\frac{5}{19}$

   Vậy x = $\frac{5}{19}$

    

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2. `a) 2/5 . x + 1/3 = 1/5`

   `<=> 2/5 x = 1/5-1/3`

   `<=> 2/5 x = -2/15`

   `<=> x = -1/3`

   Vậy `x =-1/3`

   `b) 4/9 – 5/3 . x = -2`

   `<=> – 5/3 . x = -2 -4/9`

   `<=> – 5/3 . x = -22/9`

   `<=> x = 22/15`

   Vậy `x = 22/15`

   `c) 1/5 + 5/3 : x = 1/2`

   `<=> 5/3 : x = 1/2 – 1/5`

   `<=> 5/3 : x = 3/10`

   `<=> x = 5/3 :3/10`

   `<=> x = 5/3.10/3`

   `<=> x = 50/9`

   Vậy `x = 50/9`

   `d) 5/7 : x – 3 = -2/7`

   `<=> 5/7 : x = -2/7 + 3`

   `<=> 5/7 : x = 19/7`

   `<=> x = 5/7 : 19/7`

   `<=> x = 5/19`

   Vậy `x = 5/19`

   $_Study well_$

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