Tìm x : a) 5x .(x-1/3) = 0 b) (x+1/4) . (x-3/7) = 0 c)1+3x =-5 d)1,5x – 2 ngũ 1/3x = 1.5 – 2/3 e) 2/3 + 1/3 : x = 3/5 g) (2x/3 – 3) : (-10)= 2/5

0 bình luận về “Tìm x : a) 5x .(x-1/3) = 0 b) (x+1/4) . (x-3/7) = 0 c)1+3x =-5 d)1,5x – 2 ngũ 1/3x = 1.5 – 2/3 e) 2/3 + 1/3 : x = 3/5 g) (2x/3 – 3) : (-10)= 2/5”

1. $a) 5x .(x-1/3) = 0$

   $⇒$ \(\left[ \begin{array}{l}x=0\\x=\dfrac{1}{3}\end{array} \right.\) 

       Vậy $x$ $∈$ `{0;\frac{1}{3}}`

   `b) (x+1/4) . (x-3/7) = 0`

   $⇒$ \(\left[ \begin{array}{l}x=\dfrac{-1}{4}\\x=\dfrac{3}{7}\end{array} \right.\)

       Vậy $x$ $∈$ `{\dfrac{-1}{4}; \dfrac{3}{7}}`

   $c)1+3x =-5$

   $⇔ 3x = -6$

   $⇔ x = -2$

      Vậy $x=-2$

   $d$ $1,5x – 2\dfrac{1}{3}.x = 1.5 – \dfrac{2}{3}$

   $⇔ x( \dfrac{3}{2} – \dfrac{7}{3}) = 5 – \dfrac{2}{3}$

   $⇔ x . \dfrac{-5}{6} = \dfrac{13}{3}$

   $⇔ x = \dfrac{-26}{5}$

      Vậy $x = \dfrac{-26}{5}$

   $e$) `2/3 + 1/3 : x = 3/5`

   $⇔$ `1/3 : x = 3/5 – 2/3`

   $⇔$ `1/3 : x = {-1}/15`

   $⇔$ `x = 1/3 . (-15)`

   $⇔$ `x = -5`

      Vậy $x=-5$

   $g$) ` ({2x}/3 – 3) : (-10)= 2/5`

   $⇒$ `{2x}/3 – 3 = -4`

   $⇔$ `{2x}/3 = 7`

   $⇔$ `2x = 21`

   $⇔$ $x = \dfrac{21}{2}$

      Vậy $x = \dfrac{21}{2}$

    

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2. $a)5x\left ( x-\frac{1}{3} \right )=0\\\Leftrightarrow x\left ( x-\frac{1}{3} \right )=0\\\Leftrightarrow \left[ \begin{array}{l}x=0\\x-\frac{1}{3}=0\end{array} \right.\\\Leftrightarrow \left[ \begin{array}{l}x=0\\x=\frac{1}{3}\end{array} \right.$
   Vậy $x\in \left \{ 0;\frac{1}{3} \right \}$
   $b) \left ( x+\frac{1}{4} \right )\left ( x-\frac{3}{7} \right )=0\\\Leftrightarrow \left[ \begin{array}{l}x+\frac{1}{4}=0\\x-\frac{3}{7}=0\end{array} \right.\\\Leftrightarrow \left[ \begin{array}{l}x=-\frac{1}{4}\\x=\frac{3}{7}\end{array} \right.$
   Vậy $x\in \left \{ -\frac{1}{4};\frac{3}{7} \right \}$
   $c) 1+3x=-5\\\Leftrightarrow 3x=-5-1=-6\\\Leftrightarrow x=-2$
   Vậy $x=-2$

   $d) 1,5x-2\frac{1}{3}x=1,5-\frac{2}{3}\\\Leftrightarrow \frac{3}{2}x-\frac{7}{3}x=\frac{3}{2}-\frac{2}{3}\\\Leftrightarrow -\frac{5}{6}x
   =\frac{5}{6}\\\Leftrightarrow x=-1$
   Vậy $x=-1$

   $e) \frac{2}{3}+\frac{1}{3}:x=\frac{3}{5}(ĐK:x\neq 0)\\\Leftrightarrow \frac{2}{3}+\frac{1}{3}.\frac{1}{x}=\frac{3}{5}\\\Leftrightarrow \frac{2}{3}+\frac{1}{3x}=\frac{3}{5}\\\Leftrightarrow \frac{1}{3x}=\frac{3}{5}-\frac{2}{3}\\\Leftrightarrow \frac{1}{3x}=-\frac{1}{15}\\\Leftrightarrow 3x=-15\\\Leftrightarrow x=-5$
   Vậy $x=-5$
   $g) \left ( \frac{2x}{3}-3 \right ):(-10)=\frac{2}{5}\\\Leftrightarrow \frac{2x-9}{3}.\frac{1}{-10}=\frac{2}{5}\\\Leftrightarrow -\frac{2x-9}{30}=\frac{2}{5}\\\Leftrightarrow -5(2x-9)=60\\\Leftrightarrow 2x-9=-12\\\Leftrightarrow 2x=-3\\\Leftrightarrow x=-\frac{3}{2}$

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