Recent content by jfierro

Thanks! I have revised the proof as follows, and it does seem to have gotten clearer to read. --- Facts used (implicitly or otherwise): ## 0 < a < b \to \frac{1}{b} < \frac{1}{a} ## ## a < 0 \to -a > 0 ## ## (a < b \wedge c > 0) \to ac < bc ## ## a < b < c \to a < c ## ## (-1)\frac{1}{-a} =...

Hello again. I recently submitted a thread asking for feedback on a couple of very basic proofs for an exercise from the book "How To Prove It" by Velleman. This is another request for you to help me understand how wrong my proof for a new exercise could be improved. 1. Homework Statement...

Thanks a lot. I realize the proofs are very basic so there wasn't much room for me to screw up. I just exercise 3.2.8 which was a bit more challenging and I'll post that in a new thread soon.

0. Background First and foremost, this is a proof-reading request. I'm going through Velleman's "How To Prove It" because I found that writing and understanding proofs is a prerequisite to serious study of mathematics that I did not meet. Unfortunately, the book is very light on answers to its...

Thanks, now I got the correct answer. I guess my mistake was approaching the problem from "the number of indistinguishable configurations", ignoring that some of those configurations would appear more often than others.

Conditional probability & "r balls randomly distributed in n cells" Homework Statement I'm posting this in hope that someone can give me a correct interpretation of the following problem (problem V.8 of Feller's Introduction to probability theory and its applications VOL I): 8. Seven balls...

Unfortunately, Amazon prices are targeted at the US market, where the prices are substabtially higher than in toher less developed countries. I learned multivariable calculus with Larson's book, but its listed price is 128 dollars on Amazon.com. In Mexico I got it for ~20 dollars =). It is...

Yes, don't read out loud as this is slower. Don't move your mouth when you read, simply think it in your mind, this will also save time. If you don't understand something it may be a good idea to go back a few paragraphs. Don't read when tired or hungry. Have fun.

Hmm it was indeed a problem of my vector algebra ^_^u. I was doing them by hand and when getting the imaginary part of I_CA I did only sin(-120º) and not 22sin(-120º)... I made the same mistake when constructing the matrix, the matrix should've been: \begin{bmatrix} -5j & 5j & 0 \\ 5j &...

[SOLVED] Unbalanced Three-phase circuit. Homework Statement This comes from "practice problem" 12.10 from Alexander's and Sadiku's Fundamentals of Electric circuits 3rd edition, chapter 12. The problem statement is: "Find the line currents in the unbalanced three-phase circuit of Fig...

This is from Sadiku's Elements of electromagnetics. I have come to a result but it's different from that of the book. Homework Statement Three identical small spheres of mass m are suspended by threads of negligible masses and equal length l from a common point. A charge Q is divided...

Also Born2bwire, what do you mean with freespace when you say "This is why the \beta must be less than the freespace \beta" The problem states the wave is traveling in the air and air's \epsilon and \mu are the same as for free space aren't they?

Thanks for you explanation Born2bwire, again :). This is a more intuitive response which may help me. Another thing I was thinking to do is to plug the \beta my professor says is correct into the resulting H field and then see if it complies with the Maxwell equations, that may disprove it...

Hi, I am not sure whether this falls into a math category or here, I hope you can help me. I came across a problem in a book [bare with me, please] (Fundamentals of engineering electromagnetics by Cheng) and asked my electromagnetics profesor, but his response did not help me into getting to the...

It is indeed very clear now that the contributions along the rho axis sum up to zero. Thanks :).