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Help with Geogebra

Discussion in 'Mathematics' started by lou1990lou, Jan 12, 2016.

  1. lou1990lou

    lou1990lou New commenter


    I'm getting really frustrated because I cannot find what I need... although it may just not exist which, if it is the case, is stupid!

    I am using Geogebra to demonstrate the transformation of trigonometric functions. I have everything perfect except the asymptotes of y= tan(x).
    I have used the ListAsym function, I have tried just using the Asympotote commands but I either get nothing at all or I get one asymptote.
    I want the graph to show me the asymptote at all points. Ideally I would like it so I could plot the function of f(x) = tan(x) with the asymptotes automatically showing so that when I then use the sliders on h(x) =atan((bx + c)°) I then show them how the asymptotes would move too.

    Anybody know how to fix my problem? Or if it is indeed fixable?

  2. colinbillett

    colinbillett Occasional commenter

    I gave it a shot, and like you, couldn't get a response, apart from an empty list. The help menu, online, says:
    Asymptote[ <Function> ]
    GeoGebra will attempt to find the asymptotes of the function and return them in a list. It may not find them all, for example vertical asymptotes of non-rational functions such as ln(x).
    So is tan a non-rational function? The asymptotes are vertical, so maybe what you are trying is not possible.
  3. David Getling

    David Getling Lead commenter

    Looking at the example a think what's really meant is transcendental function, rather than non-rational function. Like ln(x), tan(x) is indeed a transcendental function.
    selbelle and colinbillett like this.
  4. KYP

    KYP New commenter

    Why not put them in as a sequence of vertical lines (transformed as necessary) using the sequence command. Something like Sequence[x=pi/2+k*pi, k,0,5,1] I will try to work out the transformations for you, if you want, but it's a bit late now! You may have sorted it out anyway, by now! Do use the GeoGebra forum - you usually get a quick, expert response there!
    lou1990lou and colinbillett like this.
  5. lou1990lou

    lou1990lou New commenter

    Get in!!!
    I love it when I learn new things like this.
    I have managed to come up with the aymptotes using the sequence command and adapted it to allow them to translate when I translate tan(x) too! I just need to remember to have the asymptotes selected.

    The command I used is:
    Sequence[x = 90 + k 180 - c, k, -3, 2, 1]

    Where c is then horizontal translation.
    For anybody who may be interested I am willing to share the file, but for some reason TES won't allow me to upload it as it doesn't have a correct extension or something.
    As for asking on the Geogebra forum... I tried to sign up to do just that and it wasn't having any of it!
    colinbillett likes this.
  6. lou1990lou

    lou1990lou New commenter

    f(x) = a tan((b x + c)°) + d

    I have changed the sequence command to look like Sequence[x = 90 / b + k 180 - c + d, k, -3, 2, 1]

    As the vertical translation and y-stretching has no impact on the placement of the asymptotes
  7. lou1990lou

    lou1990lou New commenter

    Oops, made a mistake! the previous sequence would cause the transformed graph to cross over the asymptotes.

    What seems to be the correct one is:
    Sequence[x = (90 + k 180 - c) / b, k, -3, 2, 1]
    colinbillett likes this.
  8. KYP

    KYP New commenter

    Glad you've worked it out! It may be that nowadays you have to be 'accepted' as a real person on GeoGebra. Maybe if you try to upload the file onto GeoGebratube ('Share' on the File menu) you can log-in that way.

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