Answer:
C) 
Step-by-step explanation:
By the cos double angle formula, we know
Substituting
into the formula, we get
.
The answer is C.
For this case we must find the solution of the following quadratic equation:

Where:

Then, the solution is given by:

Substituting the values:

By definition we have:

Thus, we have two complex roots.
Answer:
The equation has no real roots.
Answer:
-15 + x
Step-by-step explanation: