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)