1.a) x ² -10x =0 b) 8x ²-72x=0 c)x ²+9x =0

`a, x^2-10x=0`

`<=>x.(x-10)=0`

`<=>` \(\left[ \begin{array}{l}x=0\\x-10=0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=0\\x=10\end{array} \right.\) 

 Vậy `x ∈ {0;10}`

`b,8x^2-72x=0`

`<=> 8x(x-9)=0`

`<=>` \(\left[ \begin{array}{l}8x=0\\x-9=0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=0\\x=9\end{array} \right.\) 

`c,x^2+9x=0`

`<=>x(x+9)=0`

`<=>` \(\left[ \begin{array}{l}x=0\\x+9=0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=0\\x=-9\end{array} \right.\) 

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