Graphing a Trig Function

the function is

f(x) = 3 cos [ x - (pi/2) ]

The problem that I have is with the period. I know that in y=AcosBx the period is 2pi/B but I don't quite know how to take it out of the [ x - (pi/2) ].

Also, I'd like to know what the period does exactly.
Why is it significant and what do I do with it on the graph?

 

Haven't done maths for a long time but I'll try:
f(x) = 3 cos [ x - (pi/2) ]
f(x) = 3cosx - 3cos(pi/2)
since cos(pi/2) = 0,
f(x) = 3cosx
you should know how to graph this func

 

The period is the length between the two crowns of the sinusoid.

 

Darwin, I'm looking for the PERIOD. How to find the period by just looking at the equation

Sypherz, I don't need a definition, I need a way to find it.

Anyways, I was able to find the period... It's 2*pi.

 

The subtraction doesn't affect the period, it just shifts the graph so that it looks like the graph of 3sinx