(x2- 7).(x2-49)<0
TH1: \(\Rightarrow\left\{{}\begin{matrix}x^2-7< 0\\x^2-49>0\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}x^2< 7\\x^2>49\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}x< 2\\x>7\end{matrix}\right.\)
TH2: \(\Rightarrow\left\{{}\begin{matrix}x^2-7>0\\x^2-49< 0\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}x^2>7\\x^2< 49\end{matrix}\right.\)\(\Rightarrow\left\{{}\begin{matrix}x>3\\x< 7\end{matrix}\right.\)
Vậy x<2 và x>7 hoặc x>3 và x<7
