$\"\"$

The trigonometric identity $\"\"$ .

Consider the L.H.S $\"\"$ .

Sum-to-product formulas:

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

$\"\"$

Odd and even identities: $\"italic$ and $\"italic$ .

$\"\"$

Quotient Identity: $\"\"$ .

$\"\"$

Therefore, $\"\"$ .

$\"\"$

$\"\"$ .