$\"\"$

The trigonometric function is $\"\"$ .

From the diagram : opposite side = 8 and adjacent side = 15.

Pythagorean theorem : $\"\"$ .

$\"\"$

$\"\"$ .

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

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

$\"\"$

$\"\"$ \ \

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

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