User talk:Ricardo sandoval

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Hello, Ricardo sandoval, and welcome to Wikipedia! Thank you for your contributions. I hope you like the place and decide to stay. Here are some pages that you might find helpful:

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And don't forget, the edit summary is your friend. :) – Oleg Alexandrov (talk) 16:09, 13 February 2007 (UTC)

I replied on my talk regarding Euler's formula. Oleg Alexandrov (talk) 03:17, 28 March 2007 (UTC)

Contents

[edit] Request for edit summary

When editing an article on Wikipedia there is a small field labeled "Edit summary" under the main edit-box. It looks like this:

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Filling in the edit summary field greatly helps your fellow contributors in understanding what you changed, so please always fill in the edit summary field, especially for big edits or when you are making subtle but important changes, like changing dates or numbers. Thank you. – Oleg Alexandrov (talk) 02:37, 3 April 2007 (UTC)

[edit] Euler's formula and the helix

f(x) = e^xi is a function which takes arguments from the Real line (the variable "x") giving complex values, that is, points on the complex plane (f(x) = <a,bi>), right?

(Alternatively, one could write "e^x" taking arguments directly from the Imaginary line)

You're picturing a circle on the complex plane, but that's only the range of this function. To picture the actual function (Domain x Range, Real line x Complex plane) you have to add an extra dimension (from which it takes its arguments from, its Domain).

Then you have a helix.

I hope I've made myself clearer! —The preceding unsigned comment was added by 200.164.220.194 (talk) 04:55, 17 April 2007 (UTC).

I replied on my page...

[edit] "folding"

Your way of using the word "folding" in this edit is unfamiliar to me. I've changed it to the standard term "expanding", with a link to polynomial expansion.

Can you tell me where you came across this term? Is it computer-science jargon? Michael Hardy 00:12, 30 April 2007 (UTC)

I learned the term "folding" while tutoring pre-calculus courses here at Louisiana(I am a phd student) every body seems to understand it here. So I thought it was an usual American term. But now it strikes me as weird shouldn't it be "unfolding"?
I totally agree with your edit on the Brahmagupta-Fibonacci identity. I didn't know how to make references, Thank you for showing me.
I am actually from Brasil and back there they use the expressions like "opening", "distributing", or "expanding". Its funny to see how the original meanings relate to the mathematical usage. Do you now any other terms for "expanding"? Ricardo sandoval 04:21, 30 April 2007 (UTC)

That you learned it while tutoring arouses a suspicion in my mind: It may be a corruption of "foiling", a childish term used only by those whose method of learning mathematics relies heavily on memorization. "FOIL" is an acronym for "first, outer, inner, last", used to help people remember how to expand a product of two sums: multiply the two first terms of the two factors, then the two "outer" terms, then the two "inner" terms, then the two last terms, and add them. I learned that acronym when I was an undergraduate and I was tutoring students whose approach to mathematics relied on things like that. Michael Hardy 17:21, 30 April 2007 (UTC)

My god, I totally confused myself what they really use is "foiling", nice to know the origin, but I felt bad because there is no logic in it, even thought "expanding" is the most used term I really prefer "distributing" that comes from the distributivity law and also reflects better what you actually do. For me the geometric picture is the best explanation (Area of a bigger rectangle as the sum of the four smaller ones), so that students don't have to rely on such methods and actually understand what they are doing. Ricardo sandoval 23:08, 30 April 2007 (UTC)


[edit] Proof of Cosine Law using Power of Points

Responding to your request, I'll try to produce some simplified diagrams and proofs using Power of Points theorem. Interestingly the basic technique is described in a mathematical 'pre-amble' to the seminal work of Nicolaus Copernicus: "De Revolutionibus Orbium Coelestium".

I'll work in my user sandbox and then post here so you can approve/disapprove the suggested changes as you see fit.

Neil Parker (talk) 18:35, 14 December 2007 (UTC)