The trigonometric identity on the interval .

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Apply the Sum-to-Product formula: .

Even-odd property of cosine function: .

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and .

and .

Solve these two equations separately.

Consider .

General solution for is and where .

Solutions for in are

and , where .

.

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Consider .

General solution for is and where .

Solutions for in are

and , where ....

and , where ....

and

.

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Combine above two solutions for complete solution.

  and

Arrange in ascending order.

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