Step 1:

\

The trigonometric function is $\"\"$ .

\

$\"\"$

\

Use sum formula of cosine function : $\"\"$ .

\

$\"\"$

\

$\"\"$ .

\

Substitute $\"\"$ in above trigonometric function.

\

$\"\"$

\

Use reciprocal identity : $\"\"$ .

\

$\"\"$

\

$\"\"$

\

Solution :

\

$\"\"$ .