$\"\"$

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The trigonometric equation $\"\"$ , and the interval is $\"\"$ .

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Double-angle formulas : $\"\"$ ,

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$\"\"$ (or) $\"\"$ ,

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$\"\"$ .

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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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$\"\"$

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

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Since cosine function is positive in first quadrant, $\"\"$ .

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$\"\"$

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Find $\"\"$ .

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

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$\"\"$

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$\"\"$

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The value of $\"\"$ .

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$\"\"$

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Find $\"\"$ .

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

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$\"\"$

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$\"\"$ .

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$\"\"$

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Find $\"\"$ .

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Apply Quotient identity : $\"\"$ .

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

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$\"\"$

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The value of $\"\"$ .

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$\"\"$

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$\"\"$ , $\"\"$ , and $\"\"$ .