[tex]7x^2 \ \textgreater \ 54\ \ \ |divide\ both\ sides\ by\ 7\\\\x^2 \ \textgreater \ 8\to x \ \textgreater \ \sqrt8\ \vee\ x \ \textless \ -\sqrt8\to x \ \textgreater \ 2\sqrt2\ \vee\ x \ \textless \ -2\sqrt2\\\\Answer:\boxed{x \ \textless \ -2\sqrt2\ \vee\ x \ \textgreater \ 2\sqrt2\to x\in(-\infty;-2\sqrt2)\ \cup\ (2\sqrt2;\ \infty)}[/tex]
