Answer
$(-\infty, 0]\cup [4,\infty)$; see graph.
Work Step by Step
Step 1. Rewrite the inequality as $x^2-4x\geq0$ or $x(x-4)\geq0$; the boundary points are $x=0,4$
Step 2. Using test points to examine signs across the boundary points, we have $...(+)..(0)...(-)...(4)...(+)...$; thus the solutions are $x\leq0$ plus $x\geq4$
Step 3. We can express the solutions on a real number line as shown in the figure.
Step 4. We can express the solutions in interval notation as $(-\infty, 0]\cup [4,\infty)$
