$\"\"$

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Find $\"\"$ .

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Pythagorean identity : $\"\"$ .

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Substitute $\"\"$ in above identity. \ \

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$\"\"$

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$\"\"$

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$\"\"$

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Since the angle $\"\"$ , consider the value $\"\"$ .

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Now $\"\"$ .

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Substitute corresponding values in above formula. \ \ $\"\"$

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$\"\"$

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The value of $\"\"$ .