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The trigonometric identity is $\"\"$ .

Consider $\"\"$

Rewrite the function.

$\"\"$

The sum formula for the cosine function: $\"italic$ .

The sum formula for the sine function: $\"\"$ .

$\"\"$

Divide numerator and denominator by $\"\"$ .

$\"\"$ \ \

$\"\"$

Apply quotient property: $\"\"$ .

$\"\"$

$\"\"$ .

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$\"\"$ .