This problem seems a bit out of the ordinary. s^4+ s^2-6 =0
This one won't factor, so apply the Quadratic Formula:
$\displaystyle x^2\, =\, \frac{-(3)\, \pm\, \sqrt{(3)^2\, -\, 4(1)(-6)}}{2(1)}$
$\displaystyle x^2\, =\, \frac{-3\, \pm\, \sqrt{9\, +\, 24}}{2}$
$\displaystyle x^2\, =\, \frac{-3\, \pm\, \sqrt{33}}{2}$
Then take the square root of either side to solve for "x=". Yes, you'll have some nested radicals.