$\"\"$

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The trigonometric identity is $\"\"$ .

\

Consider left hand side :

\

$\"\"$

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Apply pythagorean identity : $\"\"$ .

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$\"\"$

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Apply reciprocal identity : $\"\"$ .

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$\"\"$

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= 1

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= Right hand side identity.

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$\"\"$

\

Thus, $\"\"$ .