\(\left(5-x\right).\left(x-1\right)>0.\)
\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}5-x>0.\\x-1>0.\end{matrix}\right.\\\left\{{}\begin{matrix}5-x< 0.\\x-1< 0.\end{matrix}\right.\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x< 5.\\x< 1.\end{matrix}\right.\\\left\{{}\begin{matrix}x>5.\\x>1.\end{matrix}\right.\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x< 1.\\x>5.\end{matrix}\right.\)