$\"\"$

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The trigonometric expression is $\"\"$ .

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

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Draw one right triangle with an acute angle $\"\"$ and another with an acute angle $\"\"$ .

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Label the sides such that $\"\"$ and $\"\"$ .

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Then use the Pythagorean theorem to express the length of each third side.

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$\"\"$

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From the diagarm :

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$\"\"$ , $\"\"$ , $\"\"$ , and $\"\"$ .

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$\"\"$ .

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Apply cosine difference identity : $\"\"$ .

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$\"\"$

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Substitute the values $\"\"$ , $\"\"$ , $\"\"$ , and $\"\"$ . $\"\"$

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Therefore, $\"\"$ .

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$\"\"$

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$\"\"$ .