# Square of i

From specialfunctionswiki

## Theorem

The following formula holds: $$i^2=-1,$$ where $i$ denotes the imaginary number.

## Proof

From the definition of $i$, $$i=\sqrt{-1}.$$ Squaring both sides shows $$i^2 = \left( \sqrt{-1} \right)^2 = -1,$$ as was to be shown.