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The expression is $\"\"$ .

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Let $\"\"$ , then $\"\"$ .

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Reciprocal identity : $\"\"$ .

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$\"\"$

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Pythagorean identity : $\"\"$ .

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$\"\"$

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$\"\"$

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Difference formula of tangent function : $\"\"$ .

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$\"\"$

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Substitute $\"\"$ in above expression.

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$\"\"$

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The exact value of $\"\"$ is $\"\"$ .