Answer
$(-\infty, -1) ∪ (1, \infty)$
Work Step by Step
$$x^4>x^2$$
Subtract $x^2$
$$x^4-x^2>0$$
Factor out
$$x^2(x^2-1)>0$$
$$x^2(x-1)(x+1)>0$$
So, we have key points:
$x+1=0$ ; $x=-1$
$x=0$
$x-1=0$ ; $x=1$
Which gives us following intervals:
$(-\infty, -1)$ - Positive
$(-1, 0)$ - Negative
$(0, 1)$ - Negative
$(1, \infty)$ - Positive
We need open interval of all positive set of values, so the answer is:
$(-\infty, -1) ∪ (1, \infty)$
