$\"\"$

The expression is $\"\"$ .

Rewrite the expression.

$\"\"$ .

Consider $\"\"$ , the expression becomes $\"\"$ .

$\"\"$

From the pythegorus theorem :

$\"\"$

Therefore, $\"\"$ .

Substitue $\"\"$ in $\"\"$ .

$\"\"$

Use the properties of inverse trigonometric function: $\"\"$ .

$\"\"$ .

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

$\"\"$

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