Express cos 7pi/3 as a trigonometric function of an angle in quadrant i

To solve this problem you must apply the proccedure shown below:

 1. You want to express Cos(7π/3) as a trigonometric function of an angle in Quadrant I. Therefore, you have:
 2. You can find the coterminal angle of 7π/3 by substract 2π, as following:
 =7π/3-2π
 =π/3
 3. Then, you have:
 Cos(7π/3)
 Cos(π/3)
 The answer is: Cos(π/3)