$\"\"$

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The trigonometric equation is $\"\"$ .

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$\"\"$

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Double angle formula: $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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The general solution of $\"\"$ is $\"\"$ , where $\"\"$ is any integer.

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$\"\"$

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For $\"\"$ , $\"\"$ .

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For $\"\"$ , $\"\"$ .

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For $\"\"$ , $\"\"$ .

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Therefore, the solutions in the interval $\"\"$ are $\"\"$ .

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$\"\"$

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$\"\"$

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The solution set for $\"\"$ is $\"\"$ .