Answer
$[1,2]\cup[3,\infty)$
Work Step by Step
Step 1. The the boundary points are $x=1,2,3$
Step 2. Using test points to examine signs across the boundary points, we have
$...(-)...(1)...(+)...(2)...(-)...(3)...(+)...$
Thus the solutions are
$1\leq x\leq 2$ plus $x\geq3$
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 $[1,2]\cup[3,\infty)$
