$\"\"$

The trigonometric identity $\"\"$ .

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

Sum-to-product formulas:

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

$\"\"$

Even and odd identities: $\"italic$ and $\"italic$ .

$\"\"$

Quotient Identity: $\"\"$ .

$\"\"$ .

Therefore, $\"\"$ .

$\"\"$

$\"\"$ .