Question

Hi,
I'm trying to graph y=4cos((x/2)+(Pi/4)). So far I know:
Amplitude: 4
Period: 4Pi
Phase Shift: -Pi/2
Key Points: Pi

I know the key points for the graph y=cos(x) are:
(0,1), (Pi/2,0), (Pi,-1), (3Pi/2,0) and (2Pi,1)

How exactly do I go about finding the key points for my graph? I've tried multiplying the y values by the amplitude (4) and adding -Pi/2 to the x values, but got something different than what I copied down from the board in class. Maybe I got them down wrong, but I doubt it. They are:
(-Pi/2,4), (Pi/2,0), (3Pi/2,-4), (5Pi/2,0) and (7Pi/2,4)

Help please? Thanks!

Answer 1

Perhaps the attachment from Mathmatica 9 will help.