Question 5219
This one factors like a trinomial:

{{{x^4-10x^2+25=0}}}
{{{(x^2 - 5)(x^2 - 5) = 0 }}} or {{{ (x^2 - 5)^2 = 0 }}}


So, {{{x^2 - 5 = 0}}}


Add + 5 to each side of this equation:
{{{x^2 - 5 + 5 = 5}}}
{{{x^2 = 5}}}


Take square root of each side of the equation.  (DON'T FORGET THE + or - !!)
{{{ x = sqrt (5) }}} or {{{x = - sqrt (5)}}}


R^2 at SCC