$\"\"$

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The equation is $\"\"$ .

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$\"\"$ (Subtract $\"\"$ from each side)

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(Apply double angle formula: $\"\"$ )

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ (Take out common factor) $\"\"$

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$\"\"$ (Apply zero product property)

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ , where k is any integer. $\"\"$

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The solution is $\"\"$ , where k is any integer.