$\"\"$

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The trigonometric identity is $\"\"$ .

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Consider left hand side identity :

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$\"\"$

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$\"\"$

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Apply pythagorean identity : $\"\"$ .

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$\"\"$

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Apply reciprocal identities : $\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ .

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$\"\"$

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Thus, $\"\"$ .