Step 1:

The trigonometric function is $\"\"$ .

Consider $\"\"$ , then $\"\"$ .

From Pythagorean theorem,

$\"\"$

$\"\"$ .

Consider $\"\"$ , then $\"\"$ .

From Pythagorean theorem,

$\"\"$

Then, $\"\"$ .

Sum formula for trigonometric functions : $\"\"$ .

$\"\"$

Substitute $\"\"$ and $\"\"$ in above expression.

$\"\"$