Answer:

Step-by-step explanation:
To solve this problem you must know the formula of subtraction of angles for the function cosx.
The formula is:

We can write 30° as: 45° - 15°
Then:

Using the formula for subtraction of angles we have:

Notice that we have achieved the expression shown in the statement
Finally:

The answer would be .75. The 5 would be repeating
No because the perfect trinomial has a square as the third term and the middle term is a multiple of 2.
-9/10
thats the correct answer but you dont have that choice on your number line so???