$\"\"$

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The trigonometric identity is $\"\"$ .

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

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Apply the sum-to-product formula : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Apply odd identity: $\"italic$ .

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$\"equal$

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= Right hand side.

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$\"\"$

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$\"\"$ .