$\"\"$

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The trigonometric equation is $\"\"$ .

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The left side expression $\"\"$ .

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$\"\"$

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$\"\"$

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Reciprocal identity: $\"\"$ .

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$\"\"$

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$\"\"$

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Pythagorean identity: $\"\"$

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$\"\"$

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= Right side of the equation.

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$\"\"$

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Therefore, $\"\"$ .