$\"\"$

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The trigonometric identity is $\"\"$ .

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Consider $\"\"$ .

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Multiply and divided by $\"\"$ .

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$\"\"$

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Double angle identity: $\"\"$ .

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$\"\"$

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

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ .