# How to access/extract a specific coordinate equation from a parametric curve?

Rulatir shared this question 3 years ago

I created a tool that returns a parametric curve Curve(formula1(t),formula2(t),t,-20,20). How can I extract formula1(t) from this object without downloading the project, extracting the GGB file and hacking into xml? Is there some magic command like XEquation(curveObjectName) and YEquation(curveObjectName), just like there is Element(sequenceObjectName, number)?

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Why do you need to do that?

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I implore you! Please, first answer the original question as it was asked, even if the answer boils down to "it's not possible, full stop", and only then try to second-guess the actual intention of the person asking the question. It's not a matter of me being unwilling to take your advice. It's about doing things in the right order.

That said, I have a tool that creates a family (i.e. a sequence) of parametric curves, and I need to separately plot the y coordinate equation for one of the curves in the sequence. I can select the curve from the sequence with Element(sequence, index), but I don't know how to "recover" a coordinate equation from the curve.

The obvious workaround is to create two tools that explicitly output sequences of coordinate functions, and a third tool that takes two sequences of functions and "zips" them into parametric curves. Unless that's impossible because you can't "invoke" a function that sits in a sequence, due to the lack of universal syntax for invoking any functional value (I seem to remember reporting that as an issue). In that case I would have to create FOUR tools: two to generate sequences of "parameter sets" for the functions, one to turn a sequence of parameter sets into a sequence of function plots (hardcoding/"inlining" the function formula), and one to turn a pair of parameter set sequences into a sequence of parametric plots (hardcoding the formulas again). Is that what I will have to do? And the answer to my original, unmodified, un-reinterpreted, un-second-guessed question, is it really "this cannot be done, full stop?"

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```It's about doing things in the right order.
```

Yes, I agree. (1) You explain why you need it (2) we give up our time to answer your question if you manage (1)

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Turns out this is perfectly and directly possible. If F is a parametric curve, x(F) extracts the function that gives the x coordinate in terms of the parameter. I just didn't get the idea that something this obvious will work.

Michael Borcherds, I refuse to believe that you didn't know this answer immediately. You could have simply given it half a year ago without any whys and what-fors. Knowing you from a few interactions so far, all of which were difficult, I strongly suspect that you deliberately withheld an answer you knew, just to show who's the boss assert a principle.

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here, all like Geogebra, and try to Learn together.

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@Rulatir Passive aggressive comments are not tolerated. This is not Facebook, it's a math site where users can usually benefit of a supporting community to get help about GeoGebra.

Please don't be rude. I don't like to "act the boss" and ban people. So this is my advice. Read it as you want.

I think that asking what a tool/feature is to be used for is totally legit, and gives to who is helping you an idea on how to give the best answer. I can't send a differential equation to a preschool kid. I will send them play-doh.

P.S. You are using GeoGebra for free thanks to Michael Borcherds and a great Team of nice and collaborative people.

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I assure you that there is nothing passive about the aggression that this insufferable, intelligence-insulting "why do you need to do that" attitude provokes in me.

"Doctor, I have trouble breathing!"

"Why do you need to do that?"

Why do I need to do that? Because I need to do that, and not something else entirely! There is an atomic, elementary requirement, and I simply ask if there is a construct in the GeoGebra language that does just that.

"French teacher, how do I say good evening in French?"

"Pourquoi?"

Aaaaaaarghhhhh. There could be a language in which the correct phrase depends on the day of week, and in that case the teacher would be justified to ask about context, but French is not such a language, there is exactly one correct answer, and the teacher knows it. Yet he insists on asking, "why do you need to do that?".

Asking what a tool/feature is to be used for is totally legit. Withholding a known, direct and unambiguous answer until the person asking the question performs an entirely ritual disclosure is not legit.

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2) don't be rude to other users

3) Please assume good intentions of everyone else here

If you can't do the above then you are not welcome on this forum

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por favor, que alguien archive el hilo y se dé `por terminado

y necesito que se haga eso para no perder más mi tiempo