Question 737342
Since{{{u=x^2}}} then {{{u^2=(x^2)^2=x^4}}}
So {{{x^4 -5x^2 -14=0}}} is the same as {{{u^2 - 5u -14 = 0}}}. Which easily factors to be
{{{(u - 7)(u + 2) = 0}}}
Set each factor to zero to solve.
{{{u-7=0  or u+2 =0}}}  
This gives us u = 7 or u = -2. 

But we don't want u, we want x. Time to substitute using{{{u=x^2}}}
{{{x^2=7 or x^2=-2}}}

So we have {{{x=sqrt(7)}}}{{{x=sqrt(7)}}},{{{x=i*sqrt(2)}}},{{{x=-i*sqrt(2)}}}