The polynomial equation with root of -1 and 2i is,
[tex]\begin{gathered} (x+1)(x+2i)(x-2i)=(x+1)(x^2-(2i)^2) \\ =(x+1)(x^2-4i^2) \\ =(x+1)(x^2+4) \\ =x^3+4x+x^2+4 \\ =x^3+x^2+4x+4 \end{gathered}[/tex]
So simplest polynomial is,
[tex]x^3+x^2+4x+4[/tex]
