$\"\"$

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The function is $\"\"$ .

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From the definition of derivative

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$\"\"$

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$\"\"$

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$\"\"$ (The sum of cosine)

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$\"\"$ (Rewrite the expression)

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$\"\"$

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$\"\"$

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

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$\"\"$

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$\"\"$

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Therefore $\"\"$ .