$\"\"$

(a)

Trigonometric expression is $\"\"$ .

Observe the unit circle $\"\"$ when $\"\"$ and $\"\"$ .

Since cosine function is periodic, $\"\"$ when $\"\"$ , $\"\"$ .

$\"\"$ when $\"\"$ is an odd integer.

$\"\"$

(b)

Trigonometric expression is $\"\"$ .

Reciprocal Identity : $\"\"$ .

Observe the unit circle $\"\"$ when $\"\"$ and $\"\"$ .

$\"\"$ when $\"\"$ is an even integer.

$\"\"$

(a) $\"\"$ when $\"\"$ is an odd integer.

(b) $\"\"$ when $\"\"$ is an even integer.