plotting two functions in geogebra

djt0607 · 21-02-2017 06:48PM #1

Hi all,

I am wondering how I an plot two functions against each other in geogebra?

For example, suppose I have two functions and both are dependednt on time t

a(t) & b(t)

I wish to plot a(t) against b(t) for all time values from 0 - 1

How would I do this?

Thanks,

Regards,

djt

derb12 · 21-02-2017 06:54PM

Just plot them one after the other eg
A(x)=3x-1
B(x)=x^2
And then zoom in on the x-axis so that you are just looking between 0 and 1

djt0607 · 21-02-2017 06:59PM

Thanks for your reply.

That will only plot a(t) against t and draw another line of b(t) (against t).

I want a(t) on the y-axis against b(t) on the x-axis (or vice versa) and the graph plotted for the varying values of t

derb12 · 21-02-2017 07:48PM

I dont know what you mean by plotting functions this way - it doesn't sound like you're plotting a function.
I see you've double posted on the LC forum and here so hope you get what you're looking for over there.

djt0607 · 21-02-2017 08:48PM

Thanks again for your reply. Yes you can do it. I just did it manually anyways, so all is well and ends well.

Basically I had two functions. a(t) and b(t)

Lets say I want to find out the outputs for both functions when t=0.1.

I find a(0.1) and then b(0.1). Lets say I obtain 0.97 and 0.7

I do the same for when t=0.2

So I find a(0.2) and then b(0.2). Lets say I obtain 0.8 and 0.5

So I will have the two coordinate points

(0.97,0.7) for when t=0.1
and (0.8,0.5) for when t=0.2

I can then plot these coordinate points on a graph that will show a(t) against b(t) for varying values of t.

The two points may look something like this (assuming a(t) is the independent variable)...

b(t)
1| .
|
| .
|
|
|
|

a(t)
0 1

Geuze · 22-02-2017 12:59AM

I hope you're not a teacher.

If t is the independent variable, then it goes on the x axis.

You put t=0.1 and then t=0.2 into the two functions, okay.

But please note that your resulting co-ordinates should be of the form (0.1, f(0.1)) and (0.2, f(0.2)).

I hope that makes sense.

red_fox · 25-02-2017 10:37PM

Of course the result won't be a function, just a parameterised curve, with parameter t. I'm not experienced with geogebra but I can imagine something like plot (a(t),b(t)) for t=0..1 but I guess even ten points would give a good sense of the curve.

This is a perfectly common and sensible thing to do, and one of the more straightforward instances is in predator/prey population plots. I'm surprised you weren't met with better understanding (or maybe most just don't know how to do in Geogebra, like me!)

Edit, I'm thinking of a phase plot. Couldn't remember the name when I first posted.

plotting two functions in geogebra

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