Going around in a circle 2 pi lands you at the same spot you started...... so add or subtract multiples of 2 pi from 2pi/3 to find which of the answers is coterminal
2 pi = 6 pi /3 add or subtract multiples of this from 2 pi/3
2 pi/3 + 6pi/3 = 8 pi/3 is an answer..... do you see any more?
i think this is all?
Which angles are coterminal with an angle measure of 2π/3 ?
2π/3 - 2π = 2π/3 - 6π/3 = - 4π/3 -4π/3 -2π = -4π/3 - 6π/3 = - 10π/3
2π/3 + 2π = 2π/3 + 6π/3 = 8π/3
Here's a link where you can learn the basic about coterminal positive and negative angles.