$\"\"$

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The trigonometric expression is $\"\"$ . \ \

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Rewrite the expression.

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$\"\"$ .

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Sum rule of cosine function: $\"\"$ .

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$\"\"$

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Apply double-angle formula: $\"\"$ and $\"\"$ .

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$\"\"$

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Sum rule of sine function: $\"\"$

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$\"\"$ \ \

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Substitute $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .