Answer
$$-1\leq x \leq 1$$
Also see the image below. Blue part corresponds to the interval.
Work Step by Step
Following the solving steps of inequality, we write:
$x^2-1\leq0$
Let the expression on the left side of inequality equal to $y$
$y=x^2-1$
and graph it. See the red graph on the image above.
We need the part of the graph that lies below and including $x$-axis as we are asked for ($\leq$) in the beginning.
So our solution is $[-1, 1]$
Using interval notation: $-1\leq x \leq 1$
