$\"\"$

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The trigonometric expression is $\"\"$ .

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Consider $\"\"$ .

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The quotient identity : $\"\"$ .

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The reciprocal identity : $\"\"$ .

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$\"\"$

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$\"\"$

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Apply reciprocal identity: $\"\"$ .

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$\"\"$ .

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Option (a) matches with the expression $\"\"$ .

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$\"\"$

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(a).