Chapter R - Algebra Reference - R.5 Inequalities - R.5 Exercises - Page R-21: 39

$x^3-4x\geq0$ $x(x^2-4)\geq0$ $x(x-2)(x+2)\geq0$ $-2\leq x\leq0$ and $2\leq x$

Step 1: Factorize inequality (common factor) Step 2: Factorize expression inside the brackets (difference of squares) Step 3: The cubed function is greater than $0$ for $-2\leq x\leq0$ and $2\leq x$