Graphing this function

This is pre-calculus I believe, I'm familiar with the terms but confused on how to find what they are asking for in order to graph. Help? thank you
http://i46.tinypic.com/20p0fs.jpg

y = -(1/2)sin(3x/4)
2pi*f = 3/4
f = 3/8pi
T = one period = 8pi/3
To find zeros
-(1/2)sin(3x/4) = 0
sin(3x/4) = 0
3x/4 = 0 + k*pi where k is any integer
x = 0 and 4pi/3 and 8pi/3
So for the first positive period
Zeros are 0, 4pi/3 and 8pi/3
dy/dx = -1/2 * 3/4 * cos(3x/4) = 0 for maximum or minimum
cos(3x/4) = 0
3x/4 = pi/2 and 3pi/2
x = 2pi/3 and 2pi
y = -0.5 and 0.5)
Minima = (2pi/3,-0.5)
Maxima = (2pi,0.5)
I have uploaded an image of the graph at the link below