Answer
$x=\pm 3$
Work Step by Step
We solve by factoring:
$x^{4}-8x^{2}-9=0$
$(x^{2}-9)(x^{2}+1)=0$
$(x-3)(x+3)(x^{2}+1)=0$
$x-3=0$ or $x+3=0$ or $x^2+1=0$
$x=3$ or $x=-3$
The last equation does not have a solution, since $x^2$ can not equal $-1$. Thus the solutions are $x=\pm 3$.
