$\"\"$

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The trigonometric identity is $\"\"$ .

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The value of $\"\"$ .

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Consider right hand side : $\"\"$ .

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Substitute $\"\"$ .

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$\"\"$

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Quotient identity : $\"\"$ .

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$\"\"$

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$\"\"$ \ \ Pythagorean identity : $\"Syntax$ .

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$\"\"$

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

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$\"\"$

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$\"\"$

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= Left hand side identity.

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$\"\"$

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$\"\"$ .