Evaluate f(x)=2 square root of -9

$f (x) = 2 \sqrt{- 9}$

Simplify $2 \sqrt{- 9}$ .

Start simplifying.

$f (x) = 0 + 0 + 2 \sqrt{- 9}$

Simplify by adding zeros.

$f (x) = 2 \sqrt{- 9}$

Rewrite $- 9$ as $- 1 (9)$ .

$f (x) = 2 \sqrt{- 1 (9)}$

Rewrite $\sqrt{- 1 (9)}$ as $\sqrt{- 1} \cdot \sqrt{9}$ .

$f (x) = 2 (\sqrt{- 1} \cdot \sqrt{9})$

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

$f (x) = 2 (i \cdot \sqrt{9})$

Rewrite $9$ as $3^{2}$ .

$f (x) = 2 (i \cdot \sqrt{3^{2}})$

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

$f (x) = 2 (i \cdot 3)$

Move $3$ to the left of $i$ .

$f (x) = 2 (3 \cdot i)$

Multiply $3$ by $2$ .

$f (x) = 6 i$

Move all terms not containing $f$ to the right side of the equation.

Subtract $f (x)$ from both sides of the equation.

$0 = 6 i - f (x)$

Reorder $6 i$ and $- f (x)$ .

$0 = - f (x) + 6 i$

Rewrite the equation as $- f (x) + 6 i = 0$ .

$- f (x) + 6 i = 0$