Answer
$[1-\sqrt 2,1+\sqrt 2]$
Work Step by Step
Step 1. Rewrite the inequality as $x^2-2x-1\le0$
Step 2. Solve the equation $x^2-2x-1=0$ to get $x_1=1-\sqrt 2, x_2=1+\sqrt 2$ which are the boundary points.
Step 3. Use test points $x=-1, 0, 3$, the signs of the left side quadratic are $+, -, +$
Step 4. The inequality requires negative (middle region), thus the solution interval is $[1-\sqrt 2,1+\sqrt 2]$
