$\"\"$

The identity is $\"\"$ .

(i)

Consider left hand side identity : $\"\"$ .

Apply power reducing identity : $\"\"$ and $\"\"$ .

$\"\"$ .

$\"\"$

(ii)

Consider left hand side identity : $\"\"$ .

Apply product to sum identity : $\"\"$

$\"\"$ $\"\"$

$\"\"$

$\"\"$ .