Well!!
y = (1/2) cos (3x/4)
The graph will be of cosine terms. Let us calculate the values for one complete revolution (o to 2*pi)
x = 0 ==> y = (1/2) cos(0) = 1/2 * 1 = 1/2
x = pi/3 ==> y = (1/2) cos (pi/4) = 1/2 sqrt(2) = 1/ sqrt(8)
x = 2*pi/3 ==> y = (1/2) cos (pi/2) = 1/2 sqrt(0) = 0
x = pi ==> y = -1/2 cos (3pi/4) = -1/ sqrt(8)
x = 4pi/3 ==> y = (1/2) cos (pi) = - 1/2
x= 5pi/3 ==> y = (1/2) cos (5pi/4) = -1/ sqrt(8)
x= 2pi ==> y = (1/2) cos (3pi/2) = 0
Upon graphing, it will be like the one below:
http://www.wolframalpha.com/input/?i=y+%3D+%281%2F2%29+cos+%283x%2F4%29+