(x+5).(x-4)=0 -x(x+1)=0 9.(2x-10)=0 l-xl.lx-2l=0 3.lx-2l+2x

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1. `(x+5).(x-4)=0`

   `<=>`\(\left[ \begin{array}{l}x+5=0\\x-4=0\end{array} \right.\)

   `<=>`\(\left[ \begin{array}{l}x=-5\\x=4\end{array} \right.\)

   Vậy `x ∈  {-5,4}`

   `-x(x+1)=0`

   `<=>`\(\left[ \begin{array}{l}-x=0\\x+1=0\end{array} \right.\)

   `<=>`\(\left[ \begin{array}{l}x=0\\x=-1\end{array} \right.\)

   Vậy `x ∈ {0;-1}` 

   `9.(2x-10)=0`

   `<=>18x-90=0`

   `<=>18x=90`

   `<=>x=5`

   Vậy `x ∈ {5}`

   `|-x |.|x-2|=0`

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

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

   Vậy `x∈ {0;2}`

   `3.|x-2|+2x = 19`

   `<=>3x-6+2x=19`

   `<=>5x-6=19`

   `<=>5x=25`

   `<=>x=5`

   Vậy `x ∈ {5}`

    

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2. `a)(x+5).(x-4)=0`

   `→` \(\left[ \begin{array}{l}x+5=0\\x-4=0\end{array} \right.\) 

   `→` \(\left[ \begin{array}{l}x=-5\\x=4\end{array} \right.\) 

   Vậy `x∈{-5;4}`

   `b)-x(x+1)=0`

   `→` \(\left[ \begin{array}{l}-x=0\\x+1=0\end{array} \right.\) 

   `→` \(\left[ \begin{array}{l}x=0\\x=-1\end{array} \right.\) 

   Vậy `x∈{0;-1}`

   `c)9.(2x-10)=0`

   `→2x-10=0`

   `→2x=10`

   `→x=10:2`

   `→x=5`

   Vậy `x=5`

   `d)|-x|.|x-2|=0`

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

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

   Vậy `x∈{0;2}`

   `e)` không có kết quả.

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