Question 887314
{{{x^4+2x^2-8=0}}}
Use {{{x^2}}} as if it were the variable.   (or use a substitution for {{{x^2}}}).
{{{(x^2-2)(x^2+4)=0}}}


Either {{{x^2-2=0}}}, which gives {{{highlight(x=0+- sqrt(2))}}}
OR
{{{x^2+4=0}}}, which will give {{{x^2=-4}}}, {{{x=0+- sqrt(-4)}}}, meaning {{{highlight(x=0+- 2i)}}}