$\"\"$

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The function is $\"\"$ .

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$\"\"$

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Apply derivative on each side.

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$\"\"$

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Since the first term in $\"\"$ become $\"\"$ in $\"\"$ .

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The sum of the series $\"\"$ is same for both $\"\"$ and $\"\"$ .

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$\"\"$

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Again apply derivative on each side.

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$\"\"$ .

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$\"\"$

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Add $\"\"$ and $\"\"$ .

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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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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$ .

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$\"\"$

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$\"\"$ .