c.
\(\Leftrightarrow\left[{}\begin{matrix}x^2-2x=24\\x^2-2x=-24\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x^2-2x-24=0\\x^2-2x+24=0\left(vô.lí\right)\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-4\end{matrix}\right.\)
Vậy \(S=\left\{6;-4\right\}\)
b.
\(ĐK:x\ge5\)
\(\Leftrightarrow\left[{}\begin{matrix}5-x=x-5\\x-5=x-5\left(đúng\right)\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=10\\x\in R\end{matrix}\right.\)
Vậy \(x=10;x\in R\)
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