$\"\"$

The expression is $\"\"$ .

$\"\"$ (Apply Trigonometric identity)

$\"\"$ (Subtract $\"\"$ from each side)

$\"\"$ (Simplify)

$\"\"$ (Substitute $\"\"$ ) $\"\"$

$\"\"$ (Evaluate power: $\"\"$ )

$\"\"$ (Subtract: $\"\"$ )

$\"\"$ (Take the square root of each side)

$\"\"$ (Simplify)

$\"\"$ is in the first quadrant, cos $\"\"$ is positive,

Therefore $\"\"$ . $\"\"$

The value of $\"\"$ .