\"\"

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The identity is \"\".

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

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\"\"

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\"\" (Apply formula: \"\") \ \

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

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(Apply Pythagorean identity: \"\")

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\"\"

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\"\"

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\"\"

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\"\"     (Apply distributive property)\"\"

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\"\"  is an identity.