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The trigonometric equation is , .

Squaring on each side.

Apply double angle formula:.

Let .

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General solution of is , where is integer.

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For ,

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For ,

.

For ,

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The solutions in the interval  are and .

Check:

Substitute in .

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is not a solution of .

Substitute in .

.

is not a solution of .

Solution on interval is .

Solution set is .

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