Question 133285
Given: {{{ 3x^4-11x^2-20=0 }}}
{{{(3x + 4) (x -5) }}} 
x = -4/3   and x = 5

Given: {{{81x^4=16}}}
Take the quad root of each side
{{{3^4 * x^4 = 2^4 }}}
{{{3x = 2}}}
x = 2/3

Given: {{{ 4x^3-8x^2-x+2=0}}}
{{{4x^2(x -2) - (x-2) = 0 }}}
{{{ (4x^2 -1) (x-2) = 0}}}
{{{(2x-1)(2x+1) (x-2) = 0 }}}
x = 1/2, -1/2 , 2