$\"\"$

\

The trigonometric identity $\"\"$ .

\

Condition is $\"\"$ .

\

Trignometry formula : $\"\"$

\

$\"\"$

\

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

\

$\"\"$

\

Consider $\"\"$ .

\

Substitute $\"\"$

\

$\"\"$

\

Substitute $\"\"$ .

\

$\"\"$

\

Trigonometic identity : $\"\"$ .

\

$\"\"$

\

$\"\"$

\

$\"\"$

\

\

$\"\"$ .

\

$\"\"$

\

$\"\"$ .