Answer:
[tex]x =\sqrt{5} ,-\sqrt{5} ,-i,i[/tex]
Step-by-step solution:
[tex]0=x^4-4x^2-5[/tex] [tex]u = x^2[/tex]
[tex]0 = u^2-4u-5[/tex]
[tex]0 = (u -5)(u+1)[/tex]
[tex]u = 5[/tex] [tex]u=-1[/tex]
[tex]x^2 =5[/tex] [tex]x^2 = -1[/tex]
[tex]x= +-\sqrt{5}[/tex] [tex]x = +-i[/tex]
