The function is $\"\"$ .

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Consider $\"\"$

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Apply derivative on each side.

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$\"\"$

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Substitute $\"\"$ and $\"\"$ in the function.

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$\"\"$ \ \

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Pythagorean identity : $\"\"$ .

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$\"\"$

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$\"\"$

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Double angle identity : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$ \ \

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We know that, if $\"\"$ , then

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$\"\"$

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Substitute the values : $\"\"$ .

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$\"\"$

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$\"\"$ . \ \

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Therefore, $\"\"$ $\"\"$ .