$\"\"$

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The expression is $\"\"$ .

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From the trigonometric table $\"\"$ .

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$\"\"$

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Property of inverse trigonometry functions : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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

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$\"\"$

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