$\"\"$

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The equation is $\"\"$ .

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Consider $\"\"$ .

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Double - angle identity : $\"\"$ .

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$\"\"$

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$\"\"$ \ \

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$\"\"$ $\"\"$

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$\"\"$ \ \

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$\"\"$

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$\"\"$ \ \

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The solutions are $\"\"$ . $\"\"$

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The solutions are $\"\"$ .