$\"\"$

Observe the figure:

Adjacent side is $\"\"$ and opposite side is $\"\"$ .

Pythagorean theorem : $\"\"$ .

$\"\"$

$\"\"$ .

Basic trigonometric ratios: $\"\"$ .

$\"\"$ .

$\"\"$

Find the value of $\"\"$ .

Double angle formula : $\"\"$ .

$\"\"$

$\"\"$ .

$\"\"$

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