Решим неравенство методом интервалов.
$$ (x-4)(x+2) = 0 $$
$$ x-4 = 0 $$ или $$ x+2 = 0 $$
$$ x_1 = 4, x_2 = -2 $$
+ - +
---(-2)-----(4)-----
$$ x \in (-\infty; -2] \cup [4; +\infty) $$
Ответ: $$ x \in (-\infty; -2] \cup [4; +\infty) $$