$\"\"$

Prove that $\"\"$ .

Rewrite the above equaion : $\"\"$ .

Consider Left hand side $\"\"$ .

consider $\"\"$ then $\"\"$

$\"\"$ then $\"\"$ .

Therefore $\"\"$ .

Trigonometric angle sum identity: $\"\"$ .

Substitute $\"\"$ , $\"\"$ and $\"\"$ , $\"\"$ in the above equation

$\"\"$

$\"\"$ .