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The expression is $\"\"$ .

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Simplify $\"\"$ .

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Difference formula: $\"\"$ .

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$\"\"$

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$\"\"$

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Trigonometric identity: $\"\"$ .

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$\"\"$

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Trigonometric identity: $\"\"$ .

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$\"\"$

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Trigonometric identity: $\"\"$ .

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$\"\"$ .

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Trigonometric identity: $\"\"$ .

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$\"\"$

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Simplify:

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$\"\"$

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The exact value of $\"\"$ is $\"\"$ .