$\"\"$

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Multiply $\"\"$ by $\"\"$ .

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$\"\"$

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$\"\"$

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Difference of two squares: $\"\"$ .

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$\"\"$

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$\"\"$

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Apply Pythagorean identity: $\"\"$ .

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$\"\"$

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$\"\"$

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Cancel common terms.

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$\"\"$

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$\"\"$ $\"\"$ .

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$\"\"$

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$\"\"$ $\"\"$ .