The trigonometric equation is $\"\"$ .

$\"\"$

$\"\"$ .

Solve $\"\"$ .

The function $\"\"$ is positive in first and third quadrants.

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

$\"\"$ .

The solutions in the interval $\"\"$ are $\"\"$ .

Solve $\"\"$ .

The function $\"\"$ is negative in second and fourth quadrants.

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

$\"\"$ .

The solutions in the interval $\"\"$ are $\"\"$ .

The solution set is $\"\"$ .