Question 1174746
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{{{ x^4 - 16x^2 + 48 }}} can be 'factored' but not 'solved' 

If you had
{{{ u^2 - 16u + 48 }}}   you'd have {{{ (u-12)(u-4) }}}  so let {{{u=x^2}}} and you're mostly done:  {{{ (x^2-12)(x^2-4) }}} 

Factoring a 2nd time and simplifying, gives:
{{{ (x-2sqrt(3))(x+2sqrt(3))(x-2)(x+2) }}}