$\"\"$

The trigonometric equation is $\"\"$ .

Assume that $\"\"$ .

$\"\"$

Multiply and divide right hand side by $\"\"$ .

$\"\"$

The general solution of $\"\"$ is $\"\"$ , where $\"\"$ is an integer.

$\"\"$

Replace $\"\"$ with $\"\"$ .

$\"\"$

$\"\"$ .

$\"\"$

Solution for multiple angle equation is $\"\"$ .