\"\"

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The identity is \"\".

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To take the right hand side expression for prove that left hand side expression.

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\"\"

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\"\"   (Apply Pythagorean identity: \"\") \ \ \"\"

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\"\"  (Apply formula: \"\") \ \

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\"\"                          (Cancel common terms) \ \

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\"\"    (Apply reciprocal identity: \"\") \ \ \"\"

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\"\"  is an identity.