$\"\"$

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The trigonometric identity is $\"\"$ .

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Consider the L.H.S $\"\"$ .

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Sum-to-product formulas:

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

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$\"\"$

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Quotient Identity: $\"\"$ .

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$\"\"$

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Therefore, $\"\"$ .

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$\"\"$

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$\"\"$ .