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222-9+11+12:2*14+14 = ? ( )

Toán Lớp 7: tìm x biết (`2/3x`-`1/5`).(`3/5x`+`2/3`)<0 làm theo cách lớp 7 ạ

Toán Lớp 7: tìm x biết (2/3x-1/5).(3/5x+2/3)<0 làm theo cách lớp 7 ạ

Comments ( 2 )

  1. Giải:
    (2/3x – 1/5)(3/5x + 2/3) < 0
    -> 2/3x – 1/5 và 3/5x + 2/3 trái dấu.
    -> \(\left[ \begin{array}{l}\left\{ \begin{array}{l}\dfrac{2}{3}x – \dfrac{1}{5} < 0\\\dfrac{3}{5}x + \dfrac{2}{3} > 0\end{array} \right.\\\left\{ \begin{array}{l}\dfrac{2}{3}x – \dfrac{1}{5} >0\\\dfrac{3}{5}x + \dfrac{2}{3} < 0\end{array} \right.\end{array} \right.\) 
    ->\(\left[ \begin{array}{l}\left\{ \begin{array}{l}\dfrac{2}{3}x < \dfrac{1}{5}\\\dfrac{3}{5}x > \dfrac{-2}{3}\end{array} \right.\\\left\{ \begin{array}{l}\dfrac{2}{3}x > \dfrac{1}{5}\\\dfrac{3}{5}x < \dfrac{-2}{3}\end{array} \right.\end{array} \right.\) 
    -> \(\left[ \begin{array}{l}\left\{ \begin{array}{l}x < \dfrac{3}{10}\\x > \dfrac{-10}{9}\end{array} \right.\\\left\{ \begin{array}{l}x > \dfrac{3}{10}\\x < \dfrac{-10}{9}\ (loại)\end{array} \right.\end{array} \right.\) 
    -> (-10)/9 < x < 3/10
    Vậy (-10)/9 < x < 3/10
     

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222-9+11+12:2*14+14 = ? ( )

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