$\"\"$

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The trigonometric equation is $\"\"$ .

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Since the period of the cosine function is $\"\"$ , find the angles in the interval $\"\"$ .

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There is two angles $\"\"$ for $\"\"$ : $\"\"$ and $\"\"$ .

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

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Thus, the general solutions are $\"\"$ and $\"\"$ , where $\"\"$ is an integer.

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If $\"\"$ , then

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$\"\"$

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

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If $\"\"$ , then

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$\"\"$

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$\"\"$ and $\"\"$

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

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If $\"\"$ , then

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$\"\"$

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$\"\"$ and $\"\"$

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

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If $\"\"$ , then

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$\"\"$

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$\"\"$ and $\"\"$

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

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

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The six solutions are $\"\"$ , $\"\"$ , $\"\"$ , $\"\"$ , $\"\"$ and $\"\"$ .