[tex] {z}^{4} - 12 {z}^{2} - 64 = 0[/tex]
[tex] {z}^{2} = t[/tex]
[tex] {t}^{2} - 12t - 64 = 0[/tex]
[tex] {t}^{2} + 4t - 16t - 64 = 0[/tex]
[tex]t(t + 4) - 16(t + 4) = 0[/tex]
[tex](t - 16)(t + 4) = 0[/tex]
[tex]t - 16 = 0 = > t = 16[/tex]
[tex]t + 4 = 0 = > t = - 4[/tex]
[tex] {z}^{2} = 16 = > z = \pm \sqrt{16} = \pm4[/tex]
[tex] {z}^{2} = - 4 = > z = \pm \sqrt{ - 4} = \pm i \sqrt{4} = \pm2i[/tex]
