Question 5219
This is a typical school problem with fourth and second degree in a trinomial. They are all solved the same way. 

Use y instead of {{{x^2}}}. {{{x^4}}} is {{{y^2}}}. 

{{{y^2-10y+25=0}}}

*[invoke quadratic "y", 1, -10, 25]

As you can see, the only solution is y=5, or {{{x^2=5}}}. So, x is either {{{sqrt(5)}}}, or {{{sqrt(-5)}}}