graphing trig functions

[dash00]

i have a problem graphing trig functions such as f(x) = 2cos(3x+pi/2) -1

i know this should be very simple but i am missing something :frown:

can someone explain the way youd go about graphing this
amp= 2
period = 2pi/3
y trans = -1
x trans = (pi/2)/3 [right?]

so when i try graph it my answer is wrong, what am i missing? is it something to do with the smaller period, need help , please!

[dextercioby]

HINT: \cos \left(3x+\frac{\pi}{2}\right)=-\sin 3x

Daniel.