Question

21 решите пожалуйста

Answer 1

$x^2(-x^2-81) \leq 81(-x^2-81) \\\\ x^2(-x^2-81) -81(-x^2-81) \leq 0 \\\\ (-x^2-81)(x^2-81) \leq 0 \\\\-(x^2+81)(x^2-81) \leq 0 \\\\ (x^2+81)(x^2-81) \geq 0 \\\\ \left \{ {{x \geq 9} \atop {x \leq -9}} \right. \\\\ x \in (-\infty; -9] \cup [9;+\infty)$