Evaluate 4/( square root of 9-4^2)

$\frac{4}{\sqrt{9 - 4^{2}}}$

Simplify the denominator.

Raise $4$ to the power of $2$ .

$\frac{4}{\sqrt{9 - 1 \cdot 16}}$

Multiply $- 1$ by $16$ .

$\frac{4}{\sqrt{9 - 16}}$

Subtract $16$ from $9$ .

$\frac{4}{\sqrt{- 7}}$

Rewrite $- 7$ as $- 1 (7)$ .

$\frac{4}{\sqrt{- 1 (7)}}$

Rewrite $\sqrt{- 1 (7)}$ as $\sqrt{- 1} \cdot \sqrt{7}$ .

$\frac{4}{\sqrt{- 1} \cdot \sqrt{7}}$

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

$\frac{4}{i \sqrt{7}}$

Multiply $\frac{4}{i \sqrt{7}}$ by $\frac{\sqrt{7}}{\sqrt{7}}$ .

$\frac{4}{i \sqrt{7}} \cdot \frac{\sqrt{7}}{\sqrt{7}}$

Combine and simplify the denominator.

Multiply $\frac{4}{i \sqrt{7}}$ by $\frac{\sqrt{7}}{\sqrt{7}}$ .

$\frac{4 \sqrt{7}}{i \sqrt{7} \sqrt{7}}$

Move $\sqrt{7}$ .

$\frac{4 \sqrt{7}}{i (\sqrt{7} \sqrt{7})}$

Raise $\sqrt{7}$ to the power of $1$ .

$\frac{4 \sqrt{7}}{i ({\sqrt{7}}^{1} \sqrt{7})}$

Raise $\sqrt{7}$ to the power of $1$ .

$\frac{4 \sqrt{7}}{i ({\sqrt{7}}^{1} {\sqrt{7}}^{1})}$

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$\frac{4 \sqrt{7}}{i {\sqrt{7}}^{1 + 1}}$

Add $1$ and $1$ .

$\frac{4 \sqrt{7}}{i {\sqrt{7}}^{2}}$

Rewrite ${\sqrt{7}}^{2}$ as $7$ .

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{7}$ as $7^{\frac{1}{2}}$ .

$\frac{4 \sqrt{7}}{i {(7^{\frac{1}{2}})}^{2}}$

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$\frac{4 \sqrt{7}}{i \cdot 7^{\frac{1}{2} \cdot 2}}$

Combine $\frac{1}{2}$ and $2$ .

$\frac{4 \sqrt{7}}{i \cdot 7^{\frac{2}{2}}}$

Cancel the common factor of $2$ .

Cancel the common factor.

$\frac{4 \sqrt{7}}{i \cdot 7^{\frac{2}{2}}}$

Rewrite the expression.

$\frac{4 \sqrt{7}}{i \cdot 7^{1}}$

Evaluate the exponent.

$\frac{4 \sqrt{7}}{i \cdot 7}$

Move $7$ to the left of $i$ .

$\frac{4 \sqrt{7}}{7 i}$