$\"\"$

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Trigonometric expression is $\"\"$ .

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Coterminal angle $\"\"$ .

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where $\"\"$ is any negative or positive integer.

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Substitute $\"\"$ and $\"\"$ in $\"\"$ .

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A coterminal angle is $\"\"$ .

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The terminal side of $\"\"$ lies in Quadrant III.

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Therefore, its reference angle is $\"\"$ .

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The angle $\"\"$ in Quadrant III is negative.

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ .