\(a,M=\dfrac{2x^2-8x+6+2x^2-3x^2-6}{x\left(x-3\right)}=\dfrac{x^2-8x}{x\left(x-3\right)}=\dfrac{x\left(x-8\right)}{x\left(x-3\right)}=\dfrac{x-8}{x-3}\\ b,x=-2\Leftrightarrow M=\dfrac{-2-8}{-2-3}=\dfrac{-10}{-5}=2\\ c,M< 0\Leftrightarrow\dfrac{x-8}{x-3}< 0\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-8>0\\x-3< 0\end{matrix}\right.\\\left\{{}\begin{matrix}x-8< 0\\x-3>0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow3< x< 8\\ \Leftrightarrow x\in\left\{4;5;6;7\right\}\)
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