The function is $\"\"$ .

Apply derivative on each side with respect to $\"\"$ .

$\"\"$

$\"\"$ .

Trigonometric identity : $\"\"$ .

$\"\"$

$\"\"$ is either positive or negative over the interval $\"\"$ .

$\"\"$ over the interval $\"\"$ , since $\"\"$ .

From the I / D test, $\"\"$ on $\"\"$ .

Hence, $\"\"$ on $\"\"$ .

Therefore $\"\"$ over the interval $\"\"$ .

$\"\"$ over the interval $\"\"$ .