Question 551480
{{{ x^4 - 6x^2 - 27 = 0 }}}
Make the substitution {{{ z = x^2 }}}
{{{ z^2 - 6z - 27 - 0 }}}
{{{ ( z - 9 )*( z + 3 ) = 0 }}} ( I solved by looking at it )
{{{ z = 9 }}}
{{{ x^2 = 9 }}}
{{{ x = 3 }}}
{{{ x = -3 }}}
and
{{{ z = -3 }}}
{{{ x^2 = -3 }}}
{{{ x = sqrt(-3 ) }}}
{{{ x = sqrt(-1)*sqrt(3) }}}
{{{ x = sqrt(3)*i }}}
and
{{{ x = -sqrt(3)*i }}}
-----------------
The solutions are:
{{{ x = 3 }}}
{{{ x = -3 }}}
{{{ x = sqrt(3)*i }}}
{{{ x = -sqrt(3)*i }}}