Question

Solve the following inequation:
$x^4-5x^2+4<0$

Answer 1

$x^4-5x^2+4<0$

$\Rightarrow x^4-x^2-4x^2+4<0$

$\Rightarrow x^2(x^2-1)-4(x^2-1)<0$

$\Rightarrow (x^2-4)(x^2-1)<0$

$\Rightarrow 1<x^2<4$

Therefor, $x$ lies in $(-1,-2)\bigcup (1,2)$