We have the following expression:
[tex]-\sqrt[]{-50}[/tex]The prime factorization of 50 is
[tex]\begin{gathered} 50=2\times5\times5 \\ 50=2\times5^2 \end{gathered}[/tex]Then, we can rewritte our expression as
[tex]-\sqrt[]{-50}=-\sqrt[]{-(2\times5^2})=-i\sqrt[]{2\times5^2}[/tex]because the square root of -1 is defined as the complex i. Then, we have
[tex]\begin{gathered} -\sqrt[]{-50}=-i\times\sqrt[]{2}\times\sqrt[]{5^2} \\ or\text{ equivalently,} \\ -\sqrt[]{-50}=-i\times\sqrt[]{2}\times5 \end{gathered}[/tex]Therefore, the answer is
[tex]-\sqrt[]{-50}=-5\sqrt[]{2}\text{ i}[/tex]