Question

Find all real numbers x such that x^4 ≤ 8x^2 − 16.

Answer 1

$x^4 \leq 8x^2 -16\\ x^4-8x^2+16\leq0\\ (x^2-4)^2\leq0\\ x^2-4=0\\ x^2=4\\ x=-2 \vee x=2$