$\"\"$ \ \

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The expression is $\"\"$ .

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$\"\"$ .

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

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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Rationalize the above fraction with $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$ .

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