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### Meta

# Category Archives: Calculus/Analysis

## baby rudin

Define a real valued function on the reals by [tex] f(x):=\begin{cases} 0, & x \not\in \mathbb{Q} \\ \frac{1}{q}, & x = \frac{p}{q}, \gcd(p,q)=1, q >0 \end{cases}[/tex]. Where is this function continuous? The problem appeared in Hyman Bass’s article in the … Continue reading

Posted in Books, Calculus/Analysis
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## Speed Index

A clearly written page explaining how one can measure the speed in which a website loads by integrating the area under the curve. link

Posted in Applications, Calculus/Analysis, Web
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## 3D printing

seems to be the rage these days, and the natural question is that if there is anything that you cannot print. The short answer is NO. Thanks to Fubini’s Theorem.

Posted in Applications, Calculus/Analysis
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## Fake curves

Interesting post on how a supposed trig function is actually not trig. I have to admit I used to do things like this and use the arc tool (on powerpoint) to create curves that only look vaguely like the actual … Continue reading

Posted in Calculus/Analysis, Teaching, Technology, Trigonometry
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## Hardy on Number Theory

The elementary theory of numbers should be one of the very best subjects for early mathematical instruction. It demands very little previous knowledge; its subject matter is tangible and familiar; the processes of reasoning which it employs are simple, general … Continue reading

Posted in Calculus/Analysis, Number Theory, Quotes/People
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## gnuplot with PGF/tikz

One downside about writing calculus lecture notes has always been drawing graphs. They just take up too much time. What I used to do was to use whatever software at my disposal (usually powerpoint) and created jpeg to embed into … Continue reading

Posted in Calculus/Analysis, General, Technology
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## Manga guide to calculus

by Kojima and Togami (Illustrator). This is a follow up to the well received Manga guide to Statistics, which aims to use japanese manga to teach academic subjects. Having read the book I must say, I enjoyed the back story … Continue reading

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## Mnemonic Trig (or Trick)

[tex]\cos (3x) = 4\cos^3(x) -3 \cos(x)[/tex] The way to remember it in Hokkien (a local dialect commonly spoken in Singapore, Taiwan and southern parts of China): Cor Sah ($1.30) = Si Cor Sah ($4.30) – Sah Cor ($3). You can … Continue reading

Posted in Calculus/Analysis, Fun Stuff, Trigonometry
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## The Calculus of Friendship

by Steven Strogatz. The subtitle is “What a teacher and a student learned about life while corresponding about math” and it very aptly sums up the book. Except there is a twist. It turned out the teacher was a high … Continue reading

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## 12 Days of Christmas

Nice problem and solution at squarecirclez about counting the total number of presents. Triangular numbers appears! It seems that this year’s Simpsons Christmas special was a live action parody/tribute to Sesame Street and the Muppets. It had them singing the … Continue reading

Posted in Calculus/Analysis, Fun Stuff, Number Theory, Problems, Teaching, Technology
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## Application of Harmonic function

Cool article about Pixar and some applications of harmonic function. Would have been useful last year when I taught the maximum principle but didn’t have much else to say about it. Moving Remy in Harmony: Pixar’s Use of Harmonic Functions … Continue reading

Posted in Applications, Calculus/Analysis, Complex Numbers, Teaching, Technology
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## Breaking up is infinitely hard

I was reading this light-hearted article by jeremy au yong in the local papers. It’s mainly about how the economy is bad and he was retrenching his girlfriend. As compensation he offered a gift. The value of this gift will … Continue reading

Posted in Calculus/Analysis, Fun Stuff
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## Separating the variables

We should all be familiar with the method of separation of variables for first order ordinary differential equations. Here’s a neat example from John Starrett’s article in Amer. Math. Monthly. [tex] \displaystyle \frac{dy}{dx} = \frac{ y^3 + x^2y -x -y}{ … Continue reading

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## The Arithmetic vs Geometric Mean Trick

One classical trick is the following: Since [tex] (x -y)^2 \ge 0, [/tex] we have [tex] x^2 – 2 x y + y^2 \ge 0 \implies x^2 + 2 x y + y^2 \ge 4xy [/tex] Taking root we obtain … Continue reading

Posted in Calculus/Analysis
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## Silly Riddle

What’s the difference between jumping down from the 2nd floor versus the 20th floor? Ans: Splat! Aaaaaaahhhhh! (2nd floor) Aaaaaaaahhhhh! Splat! (20th floor) What if you jump from the 10th floor? It all depends on how long you remain in … Continue reading

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## Integration problem from pAt84

My latexrender (installed by my wife with much pain) has gone to disuse. So I’m putting up this problem posted by pAt84. Version 1 [tex]\mbox{\Large \mu = \int_0^1 \frac{ \big( \sum_{j=0}^n a_j t^j \big) \big( \sum_{i=1}^n i b_i t^i \big) … Continue reading

Posted in Calculus/Analysis, Problems
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## Stoke’s Theorem and Vector Analysis

When I first learnt this 9 years ago, I hated it. It was a “here’s the formula, use it” kind of course. Second time around, I learn the subject in the context of differential forms and boy what a world … Continue reading

Posted in Calculus/Analysis
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## Elementary Proofs

No one shall expel us from the paradise that Calculus has created. – tpc The fact that an analytic solution to number theoretical problems exist is bewildering. And often, the analytic proof is much simpler than the elementary proof. The … Continue reading

Posted in Calculus/Analysis, Number Theory, Problems
2 Comments

## Irresistible Integrals

A book by George Boros and Victor Moll. The authors bill the book as a guide to the evaluation of integrals, but it strucked me as a nice guide to old-fashioned (nineteen century) analysis, in the spirit of Gauss and … Continue reading

Posted in Books, Calculus/Analysis
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## Irritating Integral

It took me almost a week to prove [tex]\int_0^{\pi} \log (1+4\cos^2(u)) du = 2\pi \log{\phi}[/tex] where [tex]\phi = (\sqrt{5}+1)/2[/tex]. A time consuming but fruitful exercise. I had tried all the integration tricks I know, resorted to computer packages Maple and … Continue reading

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