Question 854182
{{{x^4-9x^2=20}}}


The equation is in quadratic form.
{{{x^4-9x^2-20=0}}} which seems not factorable.


Let v=x^2 and first solve for v.
{{{v^2-9v-20=0}}}
Discriminant is {{{9*9-4(-20)=81+80=161}}} and {{{161=7*23}}}.
{{{v=(9+- sqrt(161))/2}}}
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Remember how v was assigned and substituted.
{{{highlight(x=0+- sqrt((9+- sqrt(161))/2))}}}, which is itself four different expressions, four different values.



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