The trigonometric expression is $\"\"$ .

Let $\"\"$ , then $\"\"$ and $\"\"$ .

Since $\"\"$ , it follows that $\"\"$ , so $\"\"$ lies in quadrant I.

$\"\"$ .

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

The point $\"\"$ is on a circle of radius $\"\"$ .

Consider $\"\"$ .

$\"\"$

$\"\"$ .

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