Answer:
D
Step-by-step explanation:
Using cosine formula, we have
Answer:
the question is not understandable
Answer:

Step-by-step explanation:
You have the following quadratic equation given in the problem:

You must make the equation equal to zero, as following:

Add like terms:

Now, to factor the equation, you must find two numbers whose sum is -2 and whose product is -15. Therefore, you have:
