Square roots of $-i$,where $i=\sqrt{-1}$, are
1. $i,-i$
2. $cos(-\frac{\pi }{4} )+isin(-\frac{\pi }{4})+cos(\frac{3\pi }{4})+isin(\frac{3\pi }{4})$
3. $cos(\frac{\pi }{4} )+isin(\frac{3\pi }{4})+cos(\frac{3\pi }{4})+isin(\frac{\pi }{4})$
4. $cos(\frac{3\pi }{4} )+isin(-\frac{3\pi }{4})+cos(-\frac{3\pi }{4})+isin(\frac{3\pi }{4})$