$\"\"$

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The value of the trigonometric function $\"\"$ , and the interval is $\"\"$ .

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Find the value of $\"\"$ by using Pythagorean identity.

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Pythagorean identity : $\"\"$ .

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$\"\"$

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The angle $\"\"$ is in the interval $\"\"$ .

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Since cosine function is negative in third quadrant, $\"\"$ .

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$\"\"$

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Double-angle formula : $\"\"$ .

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Substitute $\"\"$ and $\"\"$ in the above double-angle formula.

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$\"\"$

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The value of $\"\"$ .

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$\"\"$

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Double-angle formula : $\"\"$ .

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Substitute $\"\"$ in the above double-angle formula.

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$\"\"$

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The value of $\"\"$ .

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$\"\"$

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Quotient identity : $\"\"$ .

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$\"\"$

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$\"\"$

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The value of $\"\"$ .

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$\"\"$

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The values of $\"\"$ .

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The value of $\"\"$ .

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The value of $\"\"$ .