Find the exact value of cos 5pi/3

1/2

Step-by-step explanation:

The angle 5pi/3 shows up in the 3rd quadrant and is equivalent to the angle 300 degrees. The "reference angle" of 300 degrees is 60 degrees; the reference angle in this case has the same trig function values as does 300 degrees. Thus, the cosine of 5pi/3 is the same as the cosine of 60 degrees, which is 1/2.