$\"\"$

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The expression is $\"\"$ .

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$\"\"$ (Apply Pythagorean identity)

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$\"\"$ (Subtract $\"\"$ from each side)

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$\"\"$ (Simplify)

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$\"\"$ (Substitute $\"\"$ )

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$\"\"$ (Evaluate power: $\"\"$ ) $\"\"$

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$\"\"$ (Subtract: $\"\"$ )

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$\"\"$ (Take the square root of each side)

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$\"\"$ (Simplify)

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$\"\"$ (Apply reciprocal identity: $\"\"$ ) \ \

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$\"\"$ (Divide: $\"\"$ ) \ \

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$\"\"$ is in the second quadrant, sec $\"\"$ is negative,

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Therefore $\"\"$ . \ \ $\"\"$

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The value of $\"\"$ .