bài 1:tìm số nguyên X ,biết a) 9.(x+28)=0 b) (27-x).(x+9) c) (-x).(x-43)=0

a/

`9(x+28) =0`

`=> x +28 =0`

`=> x = 0 -28`

`=> x = -28`

Vậy ` x = -28`

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b/

`(27-x)(x+9) =0`

`<=>` \(\left[ \begin{array}{l}27 -x =0\\x+9 =0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=27\\x=-9\end{array} \right.\) 

Vậy `x \in {27 ; -9}`

c/

`(-x)(x-43) =0`

`<=>` \(\left[ \begin{array}{l}-x =0\\x-43 =0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=0\\x=43\end{array} \right.\) 
Vậy `x \in {0 ; 43}`