# What is -square root of -100?

The square root of $- 100$ only exists as an imaginary number: $\textcolor{red}{\pm 10 i}$ where $\textcolor{b l u e}{{\textcolor{red}{i}}^{2} = - 1}$
...and for those people who believe any reference to square root should imply only the primary square root, then you can drop the minus sign: $\textcolor{red}{+ 10 i}$