Verified answer

[tex]\displaystyle\bf\\x^{2} > 81\\\\x^{2} -81 > 0\\\\x^{2} -9^{2} > 0\\\\(x-9)\cdot(x+9) > 0\\\\\\+ + + + + (-9) - - - - - (9) + + + + + \\\\\\Otvet \ x\in(-\infty \ ; \ -9) \ \cup \ (9 \ , \ +\infty)[/tex]