$\"\"$

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The expression is $\"\"$ .

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$\"\"$

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$\"\"$ ( $\"\"$ )

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$\"\"$ (Rewrite $\"\"$ )

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(Apply sum of angles formula: $\"\"$ )

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$\"\"$ $\"\"$

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(The values of $\"\"$ )

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$\"\"$

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$\"\"$ (Multiply)

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$\"\"$ (Simplify) $\"\"$

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The exact value of $\"\"$ .