ANSWER:
4th option: y = cosine (x + pi)
STEP-BY-STEP EXPLANATION:
For the function y = cosine (x), when x = 0, y = 1 and when x = , y = -1. The graph shows the opposite, when x = 0, y = -1 and when x = , y = 1, so we must add the same amount x = , for y to be positive 1.
So the equation of the graph would be:
The correct answer is then the 4th option y = cosine (x + pi)