Simplify square root of -81- square root of -144

$\sqrt{- 81} - \sqrt{- 144}$

Simplify each term.

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Rewrite $- 81$ as $- 1 (81)$ .

$\sqrt{- 1 (81)} - \sqrt{- 144}$

Rewrite $\sqrt{- 1 (81)}$ as $\sqrt{- 1} \cdot \sqrt{81}$ .

$\sqrt{- 1} \cdot \sqrt{81} - \sqrt{- 144}$

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

$i \cdot \sqrt{81} - \sqrt{- 144}$

Rewrite $81$ as $9^{2}$ .

$i \cdot \sqrt{9^{2}} - \sqrt{- 144}$

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

$i \cdot 9 - \sqrt{- 144}$

Move $9$ to the left of $i$ .

$9 \cdot i - \sqrt{- 144}$

Rewrite $- 144$ as $- 1 (144)$ .

$9 i - \sqrt{- 1 (144)}$

Rewrite $\sqrt{- 1 (144)}$ as $\sqrt{- 1} \cdot \sqrt{144}$ .

$9 i - (\sqrt{- 1} \cdot \sqrt{144})$

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

$9 i - (i \cdot \sqrt{144})$

Rewrite $144$ as $12^{2}$ .

$9 i - (i \cdot \sqrt{12^{2}})$

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

$9 i - (i \cdot 12)$

Move $12$ to the left of $i$ .

$9 i - (12 \cdot i)$

Multiply $12$ by $- 1$ .

$9 i - 12 i$

Subtract $12 i$ from $9 i$ .

$- 3 i$

Simplify square root of -81- square root of -144

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