Question 752094
{{{ 4sqrt(4-5x^2)=x }}}


Square both sides.
{{{16*(4-5x^2)=x^2}}}


Distribute the multiplication by 16.
{{{16*4-16*5x^2=x^2}}}


continuing,...


{{{16*5x^2-16*4=-x^2}}}
{{{16*5x^2+x^2-16*4=0}}}
{{{(16*5+1)x^2-16*4=0}}}
{{{81x^2-64=0}}}
{{{81x^2=64}}}
{{{x^2=64/81}}}
{{{highlight(x=8/9)}}} or {{{highlight(x=-(8/9))}}}