Given $\"\"$

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squaring on both sides

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$\"\"$

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From formula

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$\"\"$

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we can write

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$\"\"$

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$\"\"$

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$\"\"$

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We have formula

\

$\"\"$

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$\"\"$

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substitute in formula

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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By cancelling +1 and -1

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$\"\"$

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$\"\"$

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$\"\"$

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Take common 2

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$\"\"$

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We know that

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$\"\"$

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$\"\"$

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Squaring on both sides we get

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$\"\"$

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Hence it is proved that

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$\"\"$

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