$\"\"$

\

The trigonometric equation is $\"\"$ .

\

Consider left hand side of the equation : $\"\"$ .

\

$\"\"$

\

Double-angle formula : $\"\"$ .

\

$\"\"$

\

Double-angle formula : $\"\"$ .

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

Hence $\"\"$ .

\

$\"\"$

\

$\"\"$