$\"\"$

Find the exact value of the trigonometric function $\"\"$ .

From the diagram: opposite side is $\"\"$ and adjacent side is $\"\"$ .

Pythagorean theorem: $\"\"$ .

$\"\"$

The trigonometric function: $\"\"$ .

To find $\"\"$ , use half-angle formula.

Half-angle formula: $\"\"$ .

$\"\"$

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