Simplify 2* square root of -4

$2 \cdot \sqrt{- 4}$

Rewrite $- 4$ as $- 1 (4)$ .

$2 \cdot \sqrt{- 1 (4)}$

Rewrite $\sqrt{- 1 (4)}$ as $\sqrt{- 1} \cdot \sqrt{4}$ .

$2 \cdot (\sqrt{- 1} \cdot \sqrt{4})$

Rewrite $\sqrt{- 1}$ as $i$ .

$2 \cdot (i \cdot \sqrt{4})$

Rewrite $4$ as $2^{2}$ .

$2 \cdot (i \cdot \sqrt{2^{2}})$

Pull terms out from under the radical, assuming positive real numbers.

$2 \cdot (i \cdot 2)$

Move $2$ to the left of $i$ .

$2 \cdot (2 \cdot i)$

Multiply $2$ by $2$ .

$4 i$