# calcolo della derivata errato - perchè?

lemma_farkas shared this question 4 months ago

In questo file ho voluto "simulare" la corsa tra 2 runner che hanno equazioni orarie differenti. Voelvo mostrare il concetto di derivata come coeff angolare della tangente. Ho riscontrato però questo problema :

il runner rosso ha eq g(x)=4*cubicroot(x^2) e funziona tutto

il runner verde ha eq f(x)= -1+ e^(alfa x) dove alfa è un parametro settato a 0.03. Il problema è che ho chimato la costante m=f'(t) dove t è lo slider del tempo che scorre. Qui è il problema la derivata non torna . Se t=100 allroa dovremmo avere f'(100)=0.03*exp(0.03*100)= (da calcolatrice) 0,6 mentre ggb mi dà il valore di 0,74 come mai ?

Grazie mille in anticipo

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select view rounding to 10 decimals

you'll see why

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It doesn't change that much... For example if t=100, f'(100) still remains near that value, which is 0.7419170905

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rounding 10 decimals

you don't look what you have to look...

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Scrivi nell'inserimento

Derivata(f)

è esatto f'(10) = 0.7419170905

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Consider the definition of f(x).

The factor is not 0.03. The factor is 0.031570229324762.

(when check on the pocket-calculator)

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On a eu une belle journée ici en France...

Toi aussi rami..?

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I'm not sure. In quarantine, you can't see the perfidies so well.

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perfidies???

just waiting for our poster's answer...

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What is the Problem?

Maybe the language: "tückisch" in German was (automatically) translated to "perfides", which can be misleading.

But what was intended: I gave you three answers to choose from.

• For me the quarantine/lockdown is "tückisch" (because, I think, it seems to give supposed security).
• Even the unnoticed rounding is "tückisch" for me (because he is not easily recognized)
• And also your question could (conditional !!) be "tückisch" (because for me, completely out of context, And if knowingly out of context: then my anwer is comparable with your question)

You don't have to answer, but I would be interested to know why you ask me (late at night !) about the weather.

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"I would be interested to know why you ask me (late at night !) about the weather."

I give you three answers to choose from.

• I didn't watch TV to see wheather in your country
• I am a bad boy very perfide, always posting out of context
• We (mathmagic, me and you) gave enough clues to lemma_farkas, and wait for answer (and hope he find the solution : very much better he find solution than other give full solution)

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I really thank you for your suggestion

The problem involves what I called alfa, which is not exactly 0.03 as I supposed. So the exp function gets bigger and bigger with this value.

Am I right ? Or am I still wandering in the dark?

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Good... You understood

Now everything correct or it doesn't do what you want..?

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yes it does. My problem has been with my students when I illustrate the geometrica meaning. Our calculation didm't match geogerba's one. But now, thanks to all of you, I can clarify the mistery

Bye bye all of you, I really appreciate your effort

See you sono :D

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Happy for you...

Have a nice day (here today, some clouds...)