Question 784576
Factoring,
{{{ x^4-8x^2-9=0 }}} --> {{{(x^2-9)(x^2+1)=0 }}} --> {{{(x+3)(x-3)(x^2+1)=0 }}}
{{{x^2+1=0}}} has no real solutions, so we work from the other two factors
{{{x+3=0}}} --> {{{highlight(x=-3)}}}
{{{x-3=0}}} --> {{{highlight(x=3)}}}