APEXCalculus / APEXCalculusPTX

In-progress conversion of APEX Calculus to PreTeXt
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Proposed addition / modification to MVT section #150

Open grady opened 2 years ago

grady commented 2 years ago

@efrenruiz and I have some modifications/additions to the MVT section to propose.

First, we have written up the results of Sean's two videos on the corollaries of the MVT as a theorem, and placed the videos and write ups into proofs: Theorem 3.2.11: Corollaries of the Mean Value Theorem

Second, we have added a new example that applies the corollary about equivalent derivatives. Example 3.2.14: Applying a Mean Value Theorem Corollary The idea here is that showing that g(x)-h(x)=C directly would require plenty of Fun with Trig Substitutions. Conversely, the algebra showing equivalence of derivatives is pretty straightforward.

Sean's final example proving that sin(x) is Lipschitz seemed a bit abstract to us, so we wanted to do something more applied here, and "objects with the same velocity function have positions which differ by a constant" seems like a good one to us.

The second corollary is basically the same result as Theorem 5.1.4: Antiderivative Forms, so it may be worth adding something there mentioning that fact.

Any thoughts, suggestions, corrections about this new content? I can prepare a pull request if we like these changes.

sean-fitzpatrick commented 2 years ago

I think these would be a good addition: my perspective is that the MVT is primarily a theoretical result, and the main reasons to learn it in Calc 1 are to nail down some of the facts we use later on:

I don't assign the exercises currently in the book that ask students to "find the value of c" whose existence is predicted by the MVT. The one application that we discuss in class is aircraft patrol for cars speeding on the highway.

Ultimately, this one is up to @APEXCalculus. Greg, what do you think of these changes?

APEXCalculus commented 2 years ago

I didn't reply to this long ago as I wanted to think more about it. Having pondered it, and revisited it, I think the content should be added in as it adds meaningful material to the text. I would like to suggest some edits, though, supplied here via LaTeX as that's my typesetting native tongue.

Starting at https://www2.hawaii.edu/~gradysw/apex/sec_mvt.html#vidint-MVT-applications, I'd write: %%%%%%% Before ending this section, we give two important consequences of the Mean Value Theorem. Each of these consequences has important applications to mathematical theory, and can be easily understood in the context of the position and velocity of objects in motion.

First, we recall that the derivative of any constant function is zero. Is the converse true? That is, are constant functions the only ones whose derivative is zero? The Mean Value Theorem says \emph{yes}. This officially establishes our intuition about objects in (or, actually, \emph{not} in) motion: if the velocity of an object is 0, then the object's position is unchanged; it is constant.

Second, if two functions $f$ and $g$ have the same derivative, what does this tell us about $f$ and $g$? The Mean Value Theorem implies that these two functions differ only by a constant; that is, $f(x) = g(x) + C$, for some constant $C$.

This has an application to motion that is not intuitive to some. Suppose two objects start moving while 5ft. apart, and always move with the same velocity. Then the two objects will \emph{always} be 5ft. apart. (If two pennies are dropped from the 30th and 31st stories of a tall building at the same time, they will always be 1 story apart as they fall.)" %%%%%%%%

Then we introduce the Theorem/Corollary.

Example 3.2.14 ( https://www2.hawaii.edu/~gradysw/apex/sec_mvt.html#ex_application_mvt) is fine, though I'd suggest edits to the final calculation of $C$. I think this makes finding $C$ more clear. %%%%%%%%%%%% Using the equation $g(t) = h(t) + C$, we can pick any value $t\geq 0$ and use it to solve for $C$. We choose $t=0$, as that is an easy number to work with.

\begin{align} g(0) &= h(0) + C\ \tan^{-1}(1) &= -\tan^{-1}(1) + C\ \frac{\pi}{4} &= -\frac{\pi}{4} + C\ \frac{\pi}{2} &= C. \end{align} We have shown that the two objects are always $\displaystyle \frac{\pi}{2}$ units apart. %%%%%%%%%%%%%%%

Open to suggestions.

On Wed, Nov 10, 2021 at 2:25 PM Sean Fitzpatrick @.***> wrote:

I think these would be a good addition: my perspective is that the MVT is primarily a theoretical result, and the main reasons to learn it in Calc 1 are to nail down some of the facts we use later on:

  • positive/negative derivative implies increasing/decreasing
  • positive/negative second derivative implies concave up/down
  • Fundamental Theorem of Calculus (part II)
  • the arc length formula

I don't assign the exercises currently in the book that ask students to "find the value of c" whose existence is predicted by the MVT. The one application that we discuss in class is aircraft patrol for cars speeding on the highway.

Ultimately, this one is up to @APEXCalculus https://github.com/APEXCalculus. Greg, what do you think of these changes?

— You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub https://github.com/APEXCalculus/APEXCalculusPTX/issues/150#issuecomment-965667254, or unsubscribe https://github.com/notifications/unsubscribe-auth/ABT5OF4SXG43H2EB7Q5PIDTULLBI7ANCNFSM5GA5CKPQ . Triage notifications on the go with GitHub Mobile for iOS https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675 or Android https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub.

sean-fitzpatrick commented 1 year ago

I'm not sure how this issue ended up sitting for almost two years.

I don't know if @grady is still out there sitting on a pull request for us, but I can turn Grady's HTML and Greg's suggestions into some PreTeXt pretty quickly.

sean-fitzpatrick commented 1 year ago

I've written up the Theorem, and the corresponding text (most of which was already in my local version of the book).

But that's a pretty long example, so I'm going to wait to see if @grady wants to send it to me before I go to the trouble of typing it up!

APEXCalculus commented 1 year ago

Just acknowledging this; sounds good. I'll watch for a pull request when the time comes.

On Wed, Aug 2, 2023 at 5:40 PM Sean Fitzpatrick @.***> wrote:

I've written up the Theorem, and the corresponding text (most of which was already in my local version of the book).

But that's a pretty long example, so I'm going to wait to see if @grady https://github.com/grady wants to send it to me before I go to the trouble of typing it up!

— Reply to this email directly, view it on GitHub https://github.com/APEXCalculus/APEXCalculusPTX/issues/150#issuecomment-1662998959, or unsubscribe https://github.com/notifications/unsubscribe-auth/ABT5OF7EVUNW4YLWNYQZXXDXTLCNXANCNFSM5GA5CKPQ . You are receiving this because you were mentioned.Message ID: @.***>

sean-fitzpatrick commented 1 year ago

The one you just merged has everything but the example in it. ;-) There was just a lot to type up for that one...

APEXCalculus commented 1 year ago

Oops! Didn't have enough coffee yet this morning.

On Thu, Aug 3, 2023 at 11:14 AM Sean Fitzpatrick @.***> wrote:

The one you just merged has everything but the example in it. ;-) There was just a lot to type up for that one...

— Reply to this email directly, view it on GitHub https://github.com/APEXCalculus/APEXCalculusPTX/issues/150#issuecomment-1664173297, or unsubscribe https://github.com/notifications/unsubscribe-auth/ABT5OF6URMBZXG5KM6KQ2VLXTO55JANCNFSM5GA5CKPQ . You are receiving this because you were mentioned.Message ID: @.***>

sean-fitzpatrick commented 5 months ago

@grady never did send me this example...