Find the Exact Value cos(660)

Problem

cos(660)

Solution

1. Find the coterminal angle by subtracting 360 from the given angle until it is within the range [0,360)

660−360=300

2. Determine the reference angle for 300 which is located in the fourth quadrant.

(θ_ref)=360−300=60

3. Determine the sign of the cosine function in the fourth quadrant.

In Quadrant IV, *cos(θ)>0

4. Apply the reference angle to find the exact value.

cos(660)=cos(300)=cos(60)

5. Evaluate using the known value for the cosine of 60

cos(60)=1/2

Final Answer

cos(660)=1/2

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