$\"\"$

\

The expression is $\"\"$ .

\

$\"\"$ ( $\"\"$ )

\

$\"\"$ (Rewrite $\"\"$ )

\

$\"\"$ ( $\"\"$ )

\

$\"\"$ (Rewrite $\"\"$ ) \ \

\

(Apply sum of angles formula: $\"\"$ )

\

$\"\"$ $\"\"$

\

(The values of $\"\"$ )

\

$\"\"$

\

$\"\"$ (Multiply)

\

$\"\"$ (Simplify) $\"\"$

\

The exact value of $\"\"$ .