Question 646102
{{{25x^4-401x^2+16=0}}}......replace {{{-401x^2}}} with {{{-x^2-400x^2}}}

{{{25x^4-x^2-400x^2+16=0}}}

{{{25x^4-400x^2 -x^2 +16=0}}}.....group

{{{(25x^4-400x^2) -(x^2 -16)=0}}}

{{{25x^2(x^2-16) -(x^2 -16)=0}}}

{{{(x^2-16)(25x^2-1)=0}}}

{{{(x^2-4^2)((5x)^2-1)=0}}}

{{{(x-4)(x+4)(5x-1)(5x+1)=0}}}

solutions:

if 
{{{(x-4)=0}}}.......=>...{{{x=4}}}

if 
{{{(x+4)=0}}}.......=>...{{{x=-4}}}

if 
{{{(5x-1)=0}}}.......=>...{{{5x=1}}}=>...{{{x=1/5}}}

if 
{{{(5x+1)=0}}}.......=>...{{{5x=-1}}}=>...{{{x=-1/5}}}