Answer:
A. the first one
Step-by-step explanation:
First we are going to find the common denominator of both fractions. To do that, we are going to multiply their denominators:

Now we can rewrite our expression using the common denominator:

Finally, we can use the trig identities:

and

to simplify our trig expression:
We can conclude that the correct answer is the fourth one.
Answer:
9 x 4 = 36 divided by 2 = 18
An operation that is done to a value and it stays the same, it is called the "identity property".
Some quick examples:
Adding any number with zero will result in the same number.
Multiplying any number with one will result in the same number.
Hope this helps!