\[\left( x^{2} - 5 \right)^{2} + 4\left( x^{2} - 5 \right) + 3 = 0\]
\[x^{2} - 5 = y:\]
\[y^{2} + 4y + 3 = 0\]
\[D_{1} = 4 - 3 = 1\]
\[y_{1} = - 2 + 1 = - 1;\]
\[y_{2} = - 2 - 1 = - 3.\]
\[1)\ x^{2} - 5 = - 1\]
\[x^{2} = 4\]
\[x = \pm 2.\]
\[2)\ x^{2} - 5 = - 3\]
\[x^{2} = 2\]
\[x = \pm \sqrt{2}.\]
\[Ответ:x = \pm \sqrt{2};\ \ x = \pm 2.\]