Which of the following best explains why cosine startfraction 2 pi over 3 endfraction not-equals cosine startfraction 5 pi over 3 endfraction? the angles do not have the same reference angle. Cosine is negative in the second quadrant and positive in the fourth quadrant. Cosine is positive in the second quadrant and negative in the fourth quadrant. The angles do not have the same reference angle or the same sign.