$\"\"$

The expression is $\"\"$ .

Tghe definition of the inverse tangent function: If $\"\"$ , then $\"\"$ .

Write the expression interms of $\"\"$ .

$\"\"$

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

Pythagoras rule : $\"\"$ .

$\"\"$

Therefore $\"\"$ .

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

Therefore the answer is $\"\"$ .

$\"\"$

The answer is $\"\"$ .