a, Do (x - 2)(5 - x) > 0
=> x - 2; 5 - x cùng dấu
Nếu \(\left\{{}\begin{matrix}x-2>0\\5-x>0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>2\\x< 5\end{matrix}\right.\)<=> 2 < x < 5
Nếu \(\left\{{}\begin{matrix}x-2< 0\\5-x< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x< 2\\x>5\end{matrix}\right.\)(vô lý)
Vậy x = 3; 4
b, Do (x - 3)(x - 7) < 0
=> x - 3; x - 7 khác dấu
Nếu \(\left\{{}\begin{matrix}x-3>0\\x-7< 0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x>3\\x< 7\end{matrix}\right.\)<=> 3 < x < 7
Nếu \(\left\{{}\begin{matrix}x-3< 0\\x-7>0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x< 3\\x>7\end{matrix}\right.\)(vô lý)
Vậy x = 4; 5; 6
@Vũ Việt Anh
