\(\displaystyle{r}{\left({\cos{{\left(\theta\right)}}}+{i}{\sin{{\left(\theta\right)}}}\right)}\), and then you will get

\(\displaystyle{\left({r}{\left({\cos{{\left(\theta\right)}}}+{i}{\sin{{\left(\theta\right)}}}\right)}\right)}^{{\frac{{1}}{{2}}}}=\pm\sqrt{{r}}{\left({\cos{{\left(\frac{\theta}{{2}}\right)}}}+{i}{\sin{{\left(\frac{\theta}{{2}}\right)}}}\right)}\)