`(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}`
