$\"\"$

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The function is $\"\"$ .

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Apply derivative on each side with respect to $\"\"$ .

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$\"\"$

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$\"\"$

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Derivative of cotangent function : $\"\"$ .

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$\"\"$

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Trigonometric identity : $\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ .