Evaluate cos(390 degrees )

Problem

cos(390)

Solution

1. Identify the angle as being greater than 360 which means it has completed more than one full revolution around the unit circle.

2. Find the coterminal angle by subtracting 360 from the given angle to find a value within the standard range of 0 to 360

390−360=30

3. Apply the property that trigonometric functions of coterminal angles are equal.

cos(390)=cos(30)

4. Evaluate the cosine of the reference angle using the unit circle or special right triangles.

cos(30)=√(,3)/2

Final Answer

cos(390)=√(,3)/2

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