$\"\"$

\

The trigonometric equation is $\"\"$ .

\

Pythagorean identity : $\"\"$ .

\

$\"\"$

\

$\"\"$

\

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

\

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

\

Since the range of $\"\"$ is $\"\"$ , the equation $\"\"$ has no solution.

\

$\"\"$

\

Solve the equation $\"\"$ .

\

$\"\"$

\

The general solution of $\"\"$ , then $\"\"$ .

\

Where $\"\"$ .

\

Substitute $\"\"$ in $\"\"$ .

\

$\"\"$

\

Solution for $\"\"$ in the interval $\"\"$ is $\"\"$ .

\

$\"\"$

\

Solution for $\"\"$ in the interval $\"\"$ is $\"\"$ .