Step-by-step explanation:
[tex]x {}^{3} + 36x[/tex]
[tex]x( {x}^{2} + 36)[/tex]
[tex]x(x + 6i)(x - 6i)[/tex]
Set each to zero.
[tex]x = 0[/tex]
[tex]x = - 6i[/tex]
[tex]x = 6i[/tex]
