$\"\"$

Find the exact value of $\"\"$ by using double-angle formula.

Double-angle formula: $\"image\"$ .

From the figure:

$\"\"$ .

Pythagorean theorem: $\"\"$ .

$\"\"$

The trigonometric functions:

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

$\"\"$

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

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