$\"\"$

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The trigonometric function $\"\"$ .

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

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and $\"\"$ .

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Solve $\"\"$ by using Pythagorean identity.

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Pythagorean identity: $\"\"$ .

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$\"\"$

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$\"\"$ . (Since the $\"image\"$ function is positive in fourth quadrant)

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$\"\"$

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The trigonometric function $\"\"$ .

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$\"\"$ \ \

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$\"\"$

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The exact value of $\"\"$ .

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$\"\"$

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$\"\"$

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The exact value of $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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The exact value of $\"\"$ . $\"\"$

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The exact values of $\"\"$ , and $\"\"$ .