$\"\"$

\

The trigonometric function is $\"\"$ .

\

Consider $\"\"$ .

\

Apply even-odd identity : $\"\"$ .

\

$\"\"$

\

Covert the angle $\"\"$ into degrees.

\

$\"\"$ .

\

$\"\"$

\

The value of trigonometric function : $\"\"$ .

\

$\"\"$

\

$\"\"$ .

\

$\"\"$

\

The exact value of $\"\"$ .