# Thread: graphing $y=3cos(x+3pi)-2$

1. ## graphing $y=3cos(x+3pi)-2$

hoping you can help me figure this out. graphing is a little hard for me at the moment.

Find the Amplitude, the period and the phase shift for the following

$\displaystyle y=3cos(x+3pi)-2$

so far here are my answers

Amp = |3| or 3

period = $\displaystyle 2pi/1 or 2pi$

and phase shift = $\displaystyle -3pi$

the question i have is how do I start graphing this?

-4pi -3pi -2pi -pi 0 pi 2pi 3pi 4pi?

thanks!

2. Originally Posted by rasczak
$\displaystyle y=3cos(x+3pi)-2$
A major point of this type of problem is form you to figure out that things have relationships. Rather than start a new table, as if you know nothing, you are almost done.

Graph y0 = cos(x)

Graph y1 = 3cos(x) -- Just change the vertical limits from [-1,1] to [-3,3]. Done

Graph y2 = 3cos(x) - 2 -- Just change the vertical limits from [-3,3] to [-5,1]. Done

Graph y3 -- Oh, you're not going to make me do ALL the work, are you? You do this one.

Of course, when you are done, you may wish to find the x- and y- coordinate axes. They did wander around a bit.

3. Originally Posted by rasczak
hoping you can help me figure this out. graphing is a little hard for me at the moment.

Find the Amplitude, the period and the phase shift for the following

$\displaystyle y=3cos(x+3pi)-2$

so far here are my answers

Amp = |3| or 3

period = $\displaystyle 2pi/1 or 2pi$

and phase shift = $\displaystyle -3pi$

the question i have is how do I start graphing this?

-4pi -3pi -2pi -pi 0 pi 2pi 3pi 4pi?

thanks!
Attached is the graph. Use TKHunny's method to get it

Also cos(x) is plotted for contrast

4. Originally Posted by TKHunny
A major point of this type of problem is form you to figure out that things have relationships. Rather than start a new table, as if you know nothing, you are almost done.

Graph y0 = cos(x)

Graph y1 = 3cos(x) -- Just change the vertical limits from [-1,1] to [-3,3]. Done

Graph y2 = 3cos(x) - 2 -- Just change the vertical limits from [-3,3] to [-5,1]. Done

Graph y3 -- Oh, you're not going to make me do ALL the work, are you? You do this one.

Of course, when you are done, you may wish to find the x- and y- coordinate axes. They did wander around a bit.
sorry. you lost me i'm going to go back over the basics and see what i'm missing here.

5. sorry I finally got it somewhat figured out. what i had been meaning to ask was how my x axis was supposed to look.

-4pi -3pi -2pi -pi 0 pi 2pi 3pi 4pi?

Thanks for helping me figured out where I was supposed to start with regards to the y axis.

6. Really, I mean physically relabel the x- and y- axes as necessary. It will hurt, but you CAN do it.