$\"\"$

The trigonometric identity is $\"\"$ .

Consider $\"\"$

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

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

$\"\"$

Divide numerator and denominator by $\"begin$ .

$\"equal$

Apply quotient property: $\"italic$ .

$\"equal$

$\"\"$ .

$\"\"$

$\"\"$ .