$\"\"$

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The trigonometric equation is $\"\"$ .

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$\"\"$

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Apply cosine sum identity : $\"\"$ .

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$\"\"$

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$\"\"$

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Solve $\"\"$ .

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$\"\"$

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

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The solution is $\"\"$ , where $\"image\"$ is an integer.

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Now find the solutions on the interval $\"\"$ .

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If $\"\"$ , $\"\"$ .

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If $\"\"$ , $\"\"$ .

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Thus, the solutions are $\"\"$ and $\"\"$ on the interval $\"\"$ .

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$\"\"$

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The solutions of $\"\"$ are $\"\"$ and $\"\"$ on the interval $\"\"$ .