\

The trigonometric equation is $\"\"$ , $\"\"$ .

\

Squaring on each side.

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

Double angle formula: $\"\"$ .

\

$\"\"$

\

Let $\"\"$ .

\

$\"\"$

\

$\"\"$ .

\

General solution of $\"\"$ is $\"\"$ , where $\"\"$ is integer.

\

$\"\"$ .

\

For $\"\"$ ,

\

$\"\"$ .

\

For $\"\"$ ,

\

$\"\"$ .

\

For $\"\"$ ,

\

$\"\"$ .

\

Solution on interval $\"\"$ is $\"\"$ .

\

\

Solution set is $\"\"$ .