a: =>x+7=0 hoặc 8-x=0
=>x=-7 hoặc x=8
b: =>5-x=0 hoặc 6-3x=0
=>x=5 hoặc x=2
`(x+7).(8-x)=0`
`@TH1:`
`x+7=0`
`x=0-7`
`x=-7`
`@TH2:`
`8-x=0`
`x=8-0`
`x=8`
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`(-x+5).(6-3x)=0`
`@TH1:`
`-x+5=0`
`-x=0-5`
`-x=-5`
`=>x = 5`
`@TH2:`
`6-3x=0`
`3x=6-0`
`3x=6`
`x=6:3`
`x=2`
`(x + 7) (8-x) = 0`
`=>` \(\left[{}\begin{matrix}x+7=0\\8-x=0\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}x=0-7\\x=8-0\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}x=-7\\x=8\end{matrix}\right.\)
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`(-x+5)(6-3x)=0`
`=>` \(\left[{}\begin{matrix}-x+5=0\\6-3x=0\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}-x=0-5\\3x=6-0\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}-x=-5\\3x=6\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}x=5\\x=6:3\end{matrix}\right.\)
`=>` \(\left[{}\begin{matrix}x=5\\x=2\end{matrix}\right.\)
\(a)\left(x+7\right).\left(8-x\right)=0\)
\(\Rightarrow\left\{{}\begin{matrix}x+7=0\Rightarrow x=0-7=-7\\8-x=0\Rightarrow x=8-0=8\end{matrix}\right.\)
\(\text{Vậy }x\in\left(-7;8\right)\)
\(b)\left(-x+5\right).\left(6-3x\right)=0\)
\(\Rightarrow\left\{{}\begin{matrix}-x+5=0\Rightarrow-x=0-5=-5\Rightarrow x=5\\6-3x=0\Rightarrow3x=6-0=6\Rightarrow x=6:3=2\end{matrix}\right.\)
\(\text{Vậy }x\in\left\{5;2\right\}\)
