Simplify cos(210)

Problem

cos(210)

Solution

1. Identify the angle's position on the unit circle. The angle 210 is in the third quadrant because it is between 180 and 270

2. Determine the reference angle. For an angle in the third quadrant, the reference angle is found by subtracting 180 from the angle.

(θ_ref)=210−180=30

3. Apply the sign rule for the cosine function. In the third quadrant, the cosine of an angle is negative.

cos(210)=−cos(30)

4. Evaluate the cosine of the reference angle using known trigonometric values.

cos(30)=√(,3)/2

5. Combine the sign and the value to find the final result.

cos(210)=−√(,3)/2

Final Answer

cos(210)=−√(,3)/2

Want more problems? Check here!