$\"\"$

\

The trigonometric expression is $\"\"$ .

\

$\"\"$ .

\

Apply half-angle formula: $\"\"$ .

\

$\"\"$

\

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

\

$\"\"$

\

$\"\"$

\

$\"\"$ .

\

$\"\"$

\

The exact value of expression $\"\"$ .