Bài 8 : Tìm x b) x^2-5x=0 b) 5(x-2)=0 b) x(2-x)=0 b) 5(3x-21)=0

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1. Bài 8:

   a, `x^2` – 5x = 0

       x ( x – 5 )  = 0

   `=>` \(\left[ \begin{array}{l}x=0\\x-5=0\end{array} \right.\) 

   `=>` \(\left[ \begin{array}{l}x=0\\x=5\end{array} \right.\) 

       Vậy x ∈ { 0 ; 5 }

   b, 5 ( x – 2 ) = 0

            x – 2   = 0

            x         = 0 + 2

            x         = 2

      Vậy x = 2

   c, x ( 2 – x ) = 0

   `=>` \(\left[ \begin{array}{l}x=0\\2-x=0\end{array} \right.\) 

   `=>` \(\left[ \begin{array}{l}x=0\\x=2\end{array} \right.\) 

         Vậy x ∈ { 0 ; 2 }

   d, 5 ( 3x – 21 ) = 0

            3x – 21   = 0 

            3x           = 21

              x           = 7

       Vậy x = 7 

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2. $x^2-5x=0$

   $x(x-5)=0$

   `=>`\(\left[ \begin{array}{l}x=0\\x-5=0\end{array} \right.\) `=>`\(\left[ \begin{array}{l}x=0\\x=5\end{array} \right.\)

   $5(x-2)=0$

   $5x-10=0$

   $5x=0+10$

   $5x=10$

   $x=10:5$

   $x=2$

   $x(2-x)=0$

   $x(-x+2)=0$

   `=>`\(\left[ \begin{array}{l}x=0\\-x+2=0\end{array} \right.\) `=>`\(\left[ \begin{array}{l}x=0\\x=2\end{array} \right.\)

   $5(3x-21)=0$

   $15x-105=0$

   $15x=0+105$

   $15x=105$

   $x=105:15$

   $x=7$

    

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