X^4+6x^2-27=0 развернутое решение плз

$x^{4} +6 x^{2} -27=0$
$x^{2} =t$
$t^{2} +6t-27=0$

0" alt="D= b^{2} -4ac=36-4*1*(-27)=36+108=144>0" align="absmiddle" class="latex-formula">(2 корня)
$t_{1} = \frac{b+ \sqrt{D} }{2a} = \frac{-6+12}{2} = \frac{6}{2} =3$
$t_{2} = \frac{-b- \sqrt{D} }{2a} = \frac{-6-12}{2} = \frac{-18}{2} =-9$
$x_{1} = t_{2}$
$x_{2} = t_{2}$
$x_{1} =3$
$x_{2} =-9$