We know that
[tex]i=\sqrt{-1}[/tex]Then, we elevate each side to the third power
[tex]i^3=(\sqrt{-1})^3[/tex]We have to use the following power property
[tex](\sqrt{a})^b=\sqrt{a^b}[/tex]So, we have
[tex]\begin{gathered} i^3=\sqrt{(-1)^3} \\ i^3=\sqrt{-1} \end{gathered}[/tex]Since the cubic power of -1 is actually -1.
Therefore, the answer is
[tex]i^3=\sqrt{-1}[/tex]