$$6x^{4}+x^{2}-1=0$$
$x=\frac{\sqrt{3}}{3}\approx 0.577350269$
$x=-\frac{\sqrt{3}}{3}\approx -0.577350269$
$x=-\frac{\sqrt{2}i}{2}\approx -0-0.707106781i$
$x=\frac{\sqrt{2}i}{2}\approx 0.707106781i$
$x=-\frac{\sqrt{3}}{3}\approx -0.577350269$
$x=\frac{\sqrt{3}}{3}\approx 0.577350269$