Which points are on the graph of y=cos 0

a) (3n,-1) and (3pi/2, -1)
b) (2pi,1) and (pi/6, sqrt 3/2)
c) (4pi,0) and(pi/6,1/2)
d) (n,1) and (3pi/2, 0)

The correct points are:

a) (3pi/2, -1)