$\"\"$

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To find the value for $\"\"$ in third quadrant, use Pythagorean identity.

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Pythagorean identity : $\"\"$ .

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Substitute the value : $\"\"$ .

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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 value of $\"\"$ .