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[SOLVED] seek to formalize my understanding of relationships between f(x), f'(x) and f''(x)

DeusAbscondus

Active member
Jun 30, 2012
176
Hi folks,
I am seeking to hone my skills & deepen my knowledge and understanding of the relationship between f(x) and f'(x) and f''(x)

To this end, I have made a workhorse cubic with four sliders (using geogebra) attached to co-efficients a, b, c and d respectively.


My study plan is to hide f(x), manipulate the sliders (values of co-efficients) thus transforming f(x) in various ways, then trying to deduce what f(x) must now look like and trying to sketch it myself.

Two questions occur to me:

1. How can I best systemize any learnings thereby gained, in terms of rules of transformation which I can formulate, as I manipulate the co-efficients? and,


2. What principles do I need to arrive at to be a good sketcher of f(x) from f'(x)



Thanks for any help, suggestion or directions you can offer.

PS I have included inline a screenshot of the geogebra worksheet I have made and would also welcome any comments as to any errors to correct, areas of obvious improvement etc

PSS I have asked identical question in geogebraforum and am awaiting a response.
 

DeusAbscondus

Active member
Jun 30, 2012
176
In the same vein, is my comment attached to sketch below generally valid for all cubic functions and their $f'(x)$
 

Sudharaka

Well-known member
MHB Math Helper
Feb 5, 2012
1,621
Hi folks,
I am seeking to hone my skills & deepen my knowledge and understanding of the relationship between f(x) and f'(x) and f''(x)

To this end, I have made a workhorse cubic with four sliders (using geogebra) attached to co-efficients a, b, c and d respectively.


My study plan is to hide f(x), manipulate the sliders (values of co-efficients) thus transforming f(x) in various ways, then trying to deduce what f(x) must now look like and trying to sketch it myself.

Two questions occur to me:

1. How can I best systemize any learnings thereby gained, in terms of rules of transformation which I can formulate, as I manipulate the co-efficients? and,


2. What principles do I need to arrive at to be a good sketcher of f(x) from f'(x)



Thanks for any help, suggestion or directions you can offer.

PS I have included inline a screenshot of the geogebra worksheet I have made and would also welcome any comments as to any errors to correct, areas of obvious improvement etc

PSS I have asked identical question in geogebraforum and am awaiting a response.
Hi DeusAbscondus, :)

So are you trying to understand how to graph a cubic function taking into account its first and second derivatives?

Kind Regards,
Sudharaka.
 

DeusAbscondus

Active member
Jun 30, 2012
176
Hi DeusAbscondus, :)

So are you trying to understand how to graph a cubic function taking into account its first and second derivatives?

Kind Regards,
Sudharaka.
Hi Suharaka,

It's more like I want to become proficient at looking at gradient function and working out what function would look like, in basic outline; and vice-versa.

To become proficient, I presume I need to understand some generalized principles of the kind which I set forth below in my graphs (or ones like them)

So, I am asking others here if they can suggest formalized principles or generalizations of the same kind; for instance, another I've learned since making my last post is this:
if a graph is increasing across an interval, then the curvature of the second derivative will be positive; and negative, if the curve is decreasing across an interval

I want to garnish as many of these ideas as possible, generalize them into rules, make memory cards of them using geogebra and build a file of them as a study aid for my upcoming exam/test in 3 weeks.

Regs,
Deus Abs
 

Sudharaka

Well-known member
MHB Math Helper
Feb 5, 2012
1,621
Hi Suharaka,

It's more like I want to become proficient at looking at gradient function and working out what function would look like, in basic outline; and vice-versa.

To become proficient, I presume I need to understand some generalized principles of the kind which I set forth below in my graphs (or ones like them)

So, I am asking others here if they can suggest formalized principles or generalizations of the same kind; for instance, another I've learned since making my last post is this:
if a graph is increasing across an interval, then the curvature of the second derivative will be positive; and negative, if the curve is decreasing across an interval

I want to garnish as many of these ideas as possible, generalize them into rules, make memory cards of them using geogebra and build a file of them as a study aid for my upcoming exam/test in 3 weeks.

Regs,
Deus Abs
Have you come across the First derivative test and the Second derivative test? These are useful in sketching the graphs of most of the functions that you will encounter.
 

DeusAbscondus

Active member
Jun 30, 2012
176
Have you come across the First derivative test and the Second derivative test? These are useful in sketching the graphs of most of the functions that you will encounter.
Hi Sudharaka,
yes, these are the current focus of our course at school;
I was just hoping to derive a few more "tricks" to employ when looking at a function and trying to discern its gradient.

thanks for the response and the urls which are helpful,

Deus Abscondus
 

Ackbach

Indicium Physicus
Staff member
Jan 26, 2012
4,193
Hi Suharaka,

It's more like I want to become proficient at looking at gradient function and working out what function would look like, in basic outline; and vice-versa.

To become proficient, I presume I need to understand some generalized principles of the kind which I set forth below in my graphs (or ones like them)

So, I am asking others here if they can suggest formalized principles or generalizations of the same kind; for instance, another I've learned since making my last post is this:
if a graph is increasing across an interval, then the curvature of the second derivative will be positive; and negative, if the curve is decreasing across an interval

I want to garnish as many of these ideas as possible, generalize them into rules, make memory cards of them using geogebra and build a file of them as a study aid for my upcoming exam/test in 3 weeks.

Regs,
Deus Abs
You might also check out posts 8 through 11 of the Differential Calculus Tutorial. I go into a fair bit of detail in graphing functions, as that is an important application of derivatives.
 

DeusAbscondus

Active member
Jun 30, 2012
176
You might also check out posts 8 through 11 of the Differential Calculus Tutorial. I go into a fair bit of detail in graphing functions, as that is an important application of derivatives.
I will, thank you kindly.
Just the thing.

edit: 30 mins later
Just now reading through #8: love it, really! so clear.
Question Achbach: could you direct me to convenient source of help for the logical signifiers you are using with which I am unfamiliar
Example:
[FONT=MathJax_Main]lim[/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main]→[/FONT][FONT=MathJax_Main]∞[/FONT][FONT=MathJax_Math]f[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main])[/FONT][FONT=MathJax_Main]=[/FONT][FONT=MathJax_Math]L[/FONT][FONT=MathJax_Main]iff[/FONT][FONT=MathJax_Main]∀[/FONT][FONT=MathJax_Math]ϵ[/FONT][FONT=MathJax_Main]>[/FONT][FONT=MathJax_Main]0[/FONT][FONT=MathJax_Main],[/FONT][FONT=MathJax_Main]∃[/FONT][FONT=MathJax_Math]M[/FONT][FONT=MathJax_Main]>[/FONT][FONT=MathJax_Main]0[/FONT][FONT=MathJax_Main]such that if[/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main]>[/FONT][FONT=MathJax_Math]M[/FONT][FONT=MathJax_Main],[/FONT][FONT=MathJax_Main]then[/FONT][FONT=MathJax_Main]|[/FONT][FONT=MathJax_Math]f[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main])[/FONT][FONT=MathJax_Main]−[/FONT][FONT=MathJax_Math]L[/FONT][FONT=MathJax_Main]|[/FONT][FONT=MathJax_Main]<[/FONT][FONT=MathJax_Math]ϵ[/FONT][FONT=MathJax_Main].[/FONT]​
Inverted A = ? (is it like the universal: "For every ....." in this case: "For every epsilon"?
Backfacing E = ? (is it like existential quantifier: "There is a ...." in this case "There is a number M" ??

thx for the help

Regs,
Deus Abs
 
Last edited:

Mr Fantastic

Member
Jan 26, 2012
66
I will, thank you kindly.
Just the thing.

edit: 30 mins later
Just now reading through #8: love it, really! so clear.
Question Achbach: could you direct me to convenient source of help for the logical signifiers you are using with which I am unfamiliar
Example:
[FONT=MathJax_Main]lim[/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main]→[/FONT][FONT=MathJax_Main]∞[/FONT][FONT=MathJax_Math]f[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main])[/FONT][FONT=MathJax_Main]=[/FONT][FONT=MathJax_Math]L[/FONT][FONT=MathJax_Main]iff[/FONT][FONT=MathJax_Main]∀[/FONT][FONT=MathJax_Math]ϵ[/FONT][FONT=MathJax_Main]>[/FONT][FONT=MathJax_Main]0[/FONT][FONT=MathJax_Main],[/FONT][FONT=MathJax_Main]∃[/FONT][FONT=MathJax_Math]M[/FONT][FONT=MathJax_Main]>[/FONT][FONT=MathJax_Main]0[/FONT][FONT=MathJax_Main]such that if[/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main]>[/FONT][FONT=MathJax_Math]M[/FONT][FONT=MathJax_Main],[/FONT][FONT=MathJax_Main]then[/FONT][FONT=MathJax_Main]|[/FONT][FONT=MathJax_Math]f[/FONT][FONT=MathJax_Main]([/FONT][FONT=MathJax_Math]x[/FONT][FONT=MathJax_Main])[/FONT][FONT=MathJax_Main]−[/FONT][FONT=MathJax_Math]L[/FONT][FONT=MathJax_Main]|[/FONT][FONT=MathJax_Main]<[/FONT][FONT=MathJax_Math]ϵ[/FONT][FONT=MathJax_Main].[/FONT]​
Inverted A = ? (is it like the universal: "For every ....." in this case: "For every epsilon"?
Backfacing E = ? (is it like existential quantifier: "There is a ...." in this case "There is a number M" ??

thx for the help

Regs,
Deus Abs
Yes, that is more or less what they mean.
 

Ackbach

Indicium Physicus
Staff member
Jan 26, 2012
4,193
I typically read $\forall$ as "for all", and $\exists$ as "there exists". They are the universal quantifier and existential quantifier, respectively. As for a good logic website, if I were you, I would pm Evgeny.Makarov for more info - he is the undisputed logic guru around here. I'm sure he could point you in a good direction.
 

DeusAbscondus

Active member
Jun 30, 2012
176
I typically read $\forall$ as "for all", and $\exists$ as "there exists". They are the universal quantifier and existential quantifier, respectively. As for a good logic website, if I were you, I would pm Evgeny.Makarov for more info - he is the undisputed logic guru around here. I'm sure he could point you in a good direction.
'Preciate it. My formal logic from 30 years ago (an introductory course, neglected since then) is welling back up through the mists of memory, now that I turn the fading beam-pole of my attention towards the alcohol-sodden past....(Giggle)

thanks, I'll plague Evgeny (if I need to persue this further) who has already proved his worth by helping me in a number of ways.

Have a good one Ackbach,
Deus Abs