Algebra-2

Question Analysis
This problem assesses the ability to find the value of the cosine function at a specific angle.

Key Concept Explanation
The cosine function, , has specific values at key angles. For , which is in the third quadrant, the reference angle is , and the cosine value is negative.

Step-by-step Solution
1. Identify the reference angle for , which is .
2. Determine the sign of the cosine function in the third quadrant (negative).
3. Use the known value of