$\"\"$

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The trigonometric identity $\"\"$ .

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Condition is $\"\"$

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Consider $\"\"$ .

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Double angle formula : $\"\"$ .

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Sum to product formula : $\"\"$ .

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Substitute $\"\"$ in the above equation.

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$\"\"$ .

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Substitute $\"\"$ in the above equation.

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$\"\"$

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$\"\"$ \ \

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$\"\"$

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Sum to product formula : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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Trigonometric formula: $\"\"$ . \ \

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$\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ .