$\"\"$

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The trigonometric expression is $\"\"$ .

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Let $\"\"$ , then $\"\"$ .

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From Pythagorean theorem,

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$\"\"$

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$\"\"$ . $\"\"$

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Let $\"\"$ , then $\"\"$ .

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From Pythagorean theorem,

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$\"\"$

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$\"\"$ . $\"\"$

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$\"\"$ .

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Sum formula for sine function : $\"\"$ .

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$\"\"$

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$\"\"$

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Substitute $\"\"$ , $\"\"$ , $\"\"$ , $\"\"$ in above expression.

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$\"\"$

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From Inverse trigonometric functions : $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$ .