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7:00 AM
this is quite bizarre.
 
right.
and it's not like cos(1) could possibly have been negative, so it's not like I needed to include an absolute value for square rooting the square
I actually thought it might count an earlier problem I did wrong when I included the absolute value for that on my first attempt, but it counted everything right on my first try (as usual)
(I knew it technically >HAD< to have the absolute value, but I didn't know if the system would acknowledge that)
 
My reason why the stingy professor should just hire a grader.
 
(earlier problem I'm referring to, was actually more work than this problem: grab.by/fNLU )
 
Or just do it himself.
 
look, the online system is great when it works, but this is making me mad :|
 
7:03 AM
But if $t>0$ what need for $||$?!
 
eh, that's true
;)
didn't need it, but hey
I was wondering why they bothered to tack that on there, heehee
 
:)
Also, why didnt you evaluate $\cos(0)$ and
$\sin(0)$
?
For your original question, I mean.
 
I knew the system accepted it like that, so I left it so if I came back to do N and B I'd know what I had gotten for T
(easy to notice it was cos(t) and sin(t))
also, do you see where I got that sin(2) one
 
meaning?
I do understand that you used $\sin(2t)=2\sin(t)\cos(t)$, if that's what you're saying.
 
yeah
so, is there anything else I should do before I email my professor?
 
7:09 AM
Your cause seems legit to me.
 
"bitch, please, I got 100 on this assignment, the program is wrong" - your faithful student, Gnintendo"
send?
 
Hahaha. Fire!
 
I was about to email the professor, but I remembered people hang out in here
so I figured I'd have at least one "independent" review of my work before I pulled out the big guns
 
ALways good.How did you hear about M.SE?
 
oh, saw stack exchange stuff everywhere for a while
never actually used it, actually went to the site one time, was like "oh, this is cool"
saw there was a math one
was like "yay!"
about the only useful answer I've ever given, though: math.stackexchange.com/questions/145087/…
I spend most of my time tutoring people in my own classes though
 
7:12 AM
You sound like you would fit right in here :)
Your story is similar to mine.
 
I pride myself in giving concise and clear answers and explanations to people in my classes
Somebody told their friends I was a physics major as well and a group of 10 physics I students knocked on my dorm while I was answering an email about a Calculus III problem
 
Uhh Probability. I stay away from distributions and the like.
I'm a Wannabe algebraist, thankyouverymuch.
 
hehe
I had already taken AP Statistics in high school, and I used a slide rule in that class, so I had to come up with creative ways to find the area under the curve
 
Ahahaha. That sounds awesome. Huge Ego boost to be sure?
 
the method I described in that answer is actually what I used
although we didn't usually need to have that high of an accuracy, nor be that far out
so the math usually ended up being rather simple
well, I'm fine with the physics and math thing
but people figured out I wasn't taking any history or English classes because I got 5s on all the respective AP tests in high school, so now they're having me proof read their essays
and that sucks
 
7:16 AM
Does your school not have "Division requirements"?
 
It does, but I came in with 50 hours of AP credits
 
Hohoho. Nice one. :)
Now you're just binging on Math and Physics?
 
yeah...freshman? Junior by hours.
 
I was too. I did the IB, you see.
 
Well, this is first semester of 'freshman' year right now, so I have a couple of gen ed requirements left
second semester I'll be doing junior level+ math and physics exclusively
oh, and an "international dimension" credit
whatever the hell that is
 
7:18 AM
Do you plan on going to grad school for math?
Are you an international student¿?
 
quantum mechanics, ideally
and no, I'm from America
 
A pity, that.
The first, I mean.
 
:<
I really like math, though
 
America is 2 continents, you know.
;)
 
if I could I'd get a PhD in number theory and quantum mechanics
;)
(actually, I guess I can)
It's kind of a time thing.
 
7:20 AM
"Simultaneously?" is the question.
 
That would be interesting.
 
It must be late for you, if you are in OK, no?
 
yes, 2:22 AM
It's Saturday though
and there's no school on Monday (national holiday)
 
Ah! That's nice.
 
I was planning on staying up until I finished this homework
I've been on this problem on and off since about 1 AM, though
(to make sure I get a 'clean' start short-term memory wise)
 
7:23 AM
Tough guy ;)
 
I did the rest of the homework in about 30 minutes, you don't understand: I don't miss things
this was driving me INSANE
 
I think I actually understand. I go insane when that happens too. :)
You might find this question interesting:math.stackexchange.com/questions/140384/…
I answered it wrong. Try your hand at it if you want torture.
 
hm.
ogod
 
I agree. the problem is simpler when the series is $\displaystyle \sum_{i=1}^\infty \frac{\epsilon_i}{10^i}$.
 
but that's like a "duH"
 
7:32 AM
Not quite that Duh though. There is a small subtlety in it.
 
zooms
 
Fine. It is duH. :P
 
>.>
hmm
 
How would you go about it?
 
I need to word this email in mostly math
my Calculus III teacher is Japanese, he doesn't speak English very well
he's great at the math, just not talking
 
7:34 AM
Ah. Unfortunately, he needs to talk math too no?
 
right, we 'scare' numbers instead of square them, etc.
you get used to it
you just learn his pronunciation for various words and you're fine
 
Ah, and it becomes endearing after a while. When I was in Budapest, all of my professors had odd accents
and pronounced SOMEthing odd.
 
hehe
 
@Gnintendo Anyway, I must call it a day. It was nice meeting you!
Goodluck with the rest of your course.
 
thanks
I'm emailing the teacher now
 
8:16 AM
 
8:28 AM
@FortuonPaendrag Hey
 
hey BenjaLim
 
9:01 AM
Why on earth would anyone upvote this?
 
Sorry to barge in, but is anyone here interested in fielding a question on correlation?
@JayeshBadwaik, are you interested in statistics?
 
@user34522 i don't have much background in it.
If the correlation question is a simple integral something, then may be I can attempt, else if it is something deep, Imight just waste your time.
 
0
Q: Product of standard deviations

user34522If $u=cx+dy$ and $v=cx-dy$ and $R$ is the co-efficient of correlation between variables $x$ and $y$ and variables $u$ and $v$ have 0 correlation, then how can I prove that $$s_us_v=2cds_xs_y\sqrt{1-R^2}$$.I do not think I made any progress at all and I request a solution so that I can study it. ...

here it is
I am beginning to hate it.I had study a book in such a short time for my school. >.<
Automatically, my understanding is superficial.
 
@user34522 you are in high school?
 
sadly, yes
 
9:14 AM
btw, Robert Israel has tried answering your question. Do you follow his solution?
 
i am not sure.
@JayeshBadwaik,I have an exam tomorrow, :(
 
@user34522 hmm. Do you understand the first paragraph of the solution given?
You can just ask him for more clarification and let him know in comments that you are a high school student.
He will edit the solution appropriately.
 
I think I understand it.
@JayeshBadwaik, I do not think I unerstand the motivation behind considering E(u^2).
 
@user34522 are you familiar with this identity
$E((X-u)^{2}) = E(X^{2}) - u^{2}$
 
yes i am
!
@JayeshBadwaik, I am now absolutely frustrated.I am grappling with these problems since yesterday. :(
 
9:32 AM
@user34522 hmm, hard luck. I don't think I can help you too much. I haven't done much random variables for a long time.
 
@robjohn, are you interested in statisitcs?
(let me try pinging people)
 
@user34522 Probability
why do you ask?
 
I had a question on correlation.
0
Q: Product of standard deviations

user34522If $u=cx+dy$ and $v=cx-dy$ and $R$ is the co-efficient of correlation between variables $x$ and $y$ and variables $u$ and $v$ have 0 correlation, then how can I prove that $$s_us_v=2cds_xs_y\sqrt{1-R^2}$$.I do not think I made any progress at all and I request a solution so that I can study it. ...

@robjohn, is that of any interest to you?
:)
 
@user34522 Does Robert Israel's answer not suffice?
 
perhaps, my reading came in a short time and i am not familiar with this stuff.
So, it seems I cannot make much progress
 
 
11:13 AM
Rudin is obscure! Not terse, obscure.
 
11:23 AM
Whatever. Did you ever try to complete it?
I read plenty of complaints about books, but not often questions about the content!
I would say: More reading, less complaining!
3
 
@JonasTeuwen Yes, I have almost completed it.
Last two chapters remain.
Just voicing my frustration on some particular result.
 
What result?
 
11:43 AM
@JonasTeuwen I just read Riemann Rearrangement theorem from rudin and first thought it was a totally different thing than Apostol's one. Then I started reading in detail and finally worked out what he did, when he could have done it in a much more simpler way.
 
Perhaps there is a good reason to do that.
I mean often when you think: "this shit is stupid or wrong" often in the end it is you that is stupid or wrong.
 
@JonasTeuwen Yeah, trying to rack my brain about what could be it though.
Comparing the differences in two proofs right now.
He basically does an extra step of constructing a new set of sequence, while apostol doesn't why I am trying to know right now.
@skullpatrol are you have some kind of image matching algorithm developer? :-)
 
@JayeshBadwaik Maybe I am, maybe I'm not ;-)
 
hhh
Could someone help me to express planar wave?

I know how to express it in vector phone with the phase difference but struggling with the complex form, more http://en.wikipedia.org/wiki/Plane_wave:

$$U(\bar r, t) = A_0 e^{i \left( \bar k \cdot \bar r - wt + \phi \right)}$$

How can I specify the phase such as right-hand-circular-polarized in the Complex form?

P.s. Right-hand-circular-polarized means phase-difference $\phi=\pm \pi/2$ but only in $\sin$ -term or only in $\cos$ -term, not in both. If I use the complex form, I cannot see how I can express it with such as phase difference. Sho
...apparently reading wrong material, should be reading wave-equation expressed in terms of differential equations. Not sure, investigating...
 
hhh
12:16 PM
Is this a planar wave?

$$\bar E=E \left( \hat i t + \hat j \sin(kz-wt) + \hat k \cos(kz-wt+\phi) \right)$$
I think it is: it moves in i-axis -direction and oscillates in j-k -plane
 
It is not constant amplitude. Planar waves generally mean constant amplitude.
 
is there an easy and fast method for finding the coefficents of a factored polynomial?
 
@hhh if you are dealing with transverse waves, then there is no $\hat{i}$ component (no component of $\bar{E}$ in the direction of propogation, though in practice the convention is towards $\hat{k}$.
${E}$ is one vector which will co-exist with a $\bar{H}$ vector and $\bar{S} = \bar{E} \times \bar{H}$ and the direction of propogation is the direction of $\bar{S}$.
So, you $\bar{E}$ will only be $E \left( \hat j \sin(kz-wt) + \hat k \cos(kz-wt+\phi) \right)$
Circular Polarized means the $\bar{H}$ is always perpendicular and equal in magnitude to $\bar{E}$
 
@MaoYiyi Do you have an example?
 
12:32 PM
The $\phi$ you have has more to do with the phase due to delay of propogation in both $\bar{E}$ and $\bar{H}$
 
@skullpatrol (x-7)^8 (x-5)^20, something like that.
 
(According to the original equations that is)
@hhh original means these.
\begin{equation}
U(\bar r, t) = A_0 e^{i \left( \bar k \cdot \bar r - wt + \phi \right)}
\end{equation}
 
@skullpatrol I know I could do binomal expandsion but then I still need to multiply the terms.
is anyone here?
 
Maybe try writing x-7 as x-5-2, then sub in a=x-5
(a-2)^8 a^20
Then expand and multiply.
@MaoYiyi Does that help?
 
12:48 PM
@skullpatrol yes, somewhat. just was hoping there was some nice formula for doing this for any given factored polynomial.
 
Not that I know of.
 
@skullpatrol thanks.
do you think it would be a good idea if there were multiple answers to a question to randomly list them in order if they have the same upvotes?
 
I would prefer to list them chronologically in that case.
 
1:07 PM
@skullpatrol why chronologically?
 
hhh
My book mentions that

1. if $\phi=\pm\pi/2$, then the polarisation is circular
2. if $\phi=0$, then the polarisation is linear

P.556-557, Understanding Physics.
@JayeshBadwaik So hence confused about this $\phi$ in the complex form. The $\phi$ is in both $\sin$ and $\cos$ -terms, not so in the non-complex -form.
Q here, physically.
 
@MaoYiyi To me, it seems fairer than randomly.
Speed should count for something :)
 
1:26 PM
@skullpatrol yes, i see your point; but, sometimes it just which one gets posted first.
 
@hhh the equation you have is about more complex waves than just normal plane waves
 
hhh
?
But they are both still about "planar waves"?
 
is the book understanding physics by hulton et al?
@hhh he is probably talking about a different $\phi$ and the notation must have been confused.
 
hhh
@JayeshBadwaik By Michael Mansfiedld and Colm O'Sullivan.
 
Is it possible for you to take a photo and upload it here, directly from the book?
 
hhh
1:30 PM
Wiley Praxis
 
@MaoYiyi Yes, I agree and allowing for edits complicates matters.
 
@skullpatrol that is why I think they should be random because of reading fatigue. Who really scrolls all the way down.
 
hhh
@JayeshBadwaik There it mentions when the equations correspond to linear/circular -cases but I was asked to provide equation in "planar form" but not sure whether it needs to be expressed in terms of complex numbers...
 
@hhh so the book has given the equation correctly that is
$\bar{E} = E \left( \hat j \sin(kz-wt) + \hat k \cos(kz-wt+\phi) \right)$
 
hhh
The book does not mention the general case with elliptic polarization.
 
1:37 PM
Now you want to convert this equation to planar form right?
 
hhh
Yes.
 
Generally, I believe answers should be put in an order determined by the preferences of the question asker and not by voters, since the question asker is the one who is trying to understand the answers, but that is just my humble opinion @MaoYiyi
 
@hhh has your professor said something about planar form? Like what he wants from it?
I don't think that is a standard notation.
 
@hhh how did you post the picture?
@skullpatrol yes, that is what the accepted answer is for I thought.
 
hhh
Nothing, just requirement to have "planar" wave. I am not sure whethere this is the right form:

$$\bar{E} = E \left( \hat j \sin(kz-wt) + \hat k \cos(kz-wt+\phi) \right)$$
or the complex form, ideas?
 
1:41 PM
No that is incorrect.
I am guessing that he simply means equation of a circle.
 
hhh
@MaoYiyi I used Android -phone through Wifi to upload the picture and then just copied it here.
 
@MaoYiyi But after the accepted answer, the voters get to decide in what order the answers will be posted.
 
hhh
One of my friends suggested me to use Wave-equation with differential-equations.

...now more than confused what is looked for with this "planar form".
 
@skullpatrol didn't know that.
 
@hhh simply ask your prof. I think there is not much to it.
 
1:44 PM
@hhh thanks, didn't know that was possible.
 
He might have wanted to write polar.
and wrote planar instead
the polar form can be this
http://chat.stackexchange.com/transcript/message/6003965#6003965
 
hhh
@MaoYiyi Perhaps interesting to you: android.stackexchange.com/questions/28479/…
 
@JayeshBadwaik Two group theory questions for me today :D
 
@BenjaLim ?
 
1:59 PM
@JayeshBadwaik I answered two today :D
 
@BenjaLim Nice. :D
 
 
2 hours later…
3:49 PM
Lets see if this latex works: $$7 \pi -\text{Log}\left[\frac{3}{2} e^{-3 \pi /2}+e^{5 \pi /2}+2 \pi \right]=14.13472554011971250976196...$$
 
@Mats It displays correct for me
 
up to those zeta zeroes again are we?
 
yes, I should stop
 
@anon Dawg.
@hhh Cooooooooooool!
@anon Anuun.
 
what?
 
4:01 PM
@anon Could you explain to me what is the formal definition of "class" vs "set"? =)
 
@PeterTamaroff I'm sure we had a question about this in the last two weeks. I answered it.
 
No, the formal distinction has something to do with predicates or model theory or blah that I don't know about. The informal distinction is that classes are bigger.
 
@ZhenLin Could you help?
 
See here.
 
@ZhenLin Great answer. Is your name Lin, Zhen, Zhen Lin, or non of the former?
 
4:07 PM
You can call me Zhen Lin.
 
@ZhenLin I guess I'll be able take the most of it after some more college studies.
 
shrug
It's not an important distinction if you're not concerned about formal mathematics.
 
@ZhenLin Maybe I am =)
Time will tell.
 
I have recently been wondering if I should be using Ackermann set theory... it seems more convenient than having just one kind of proper class, like in NBG or MK.
 
@ZhenLin I can't help you in the wondering... =P
 
4:19 PM
Is there a name for the category of extensions of a given field K with morphisms those injective field homomorphisms that fix the base field?
I'm looking up some galois theory and it seems to work with those kind of diagrams a lot.
 
All field homomorphisms are injective. You can just call it the category of field extensions of $K$. Or you can write $K / \textbf{Fld}$ or something...
 
Hmm, this text uses $\mathrm{Mono}_K(L,F)$ for monomorphisms $L\to F$ that fix a base field $K$ (obviously with $L,F/K$ extensions). I guess it's unnecessary to specify mono - it might as well just be $\hom_K$ for all field homomorphisms fixing $K$. I see that if a map between fields isn't injective then the kernel is nontrivial and $f(u)=0\implies f(1)=f(u^{-1}u)=0\ne1$, an impossibility.
 
Well, perhaps $\textrm{Hom}_K$ looks too much like $K$-linear maps between vector spaces...
 
that's probably why, yeah
 
5:11 PM
Happy to note that we have John Senior.
@Jonas Yes, I have learnt this More Reading, less complaining art....
 
5:38 PM
Hmm, it's quiet in here. So, I'll be here later...
 
Hi folks
 
5:56 PM
@JohnSenior Hello.
I just sent a first draft of my Bsc's thesis to my supervisor.
 
seems very quiet in here recently
@Matt Excellent! - hope he likes it
 
@JohnSenior too quiet
 
It's quite unfinished.
But yes, I also hope he likes it.
I like quiet.
The only thing that I don't like is that the teddy is absent.
 
@Matt I am sure he will suggest things to add to it :)
 
@JohnSenior Do we need to add a sound feed here? :-D
 
5:58 PM
: )
 
@robjohn LOL
 
It would be interesting to see if we could ever agree on any music to listen to.
 
How about Jack Johnson?
Or Bach?
Or Beatles!
 
@robjohn I very much doubt it
 
@JohnSenior I do, too.
 
6:02 PM
I would probably turn off anything that isn't classical
 
@robjohn Did you mean the three of us or all chat room users?
 
@Matt I was thinking of the chat room users
 
Ok, that makes it slightly more difficult.
 
We three could settle on classical probably
 
Sure.
 
6:03 PM
I used to hate very modern classical stuff, but Jonas has almost converted me to some of it at least
 
I don't know where @anon's preferences in music lie.
Mine are fairly broad, but some of the more modern genres take some filtering and getting used to.
 
: )
 
Anyone here know anything about class field theory?
 
@JohnSenior Not I
 
Me neither - yet - but I am trying to find out something about it, and struggling
Hi @KannappanSampath
 
6:08 PM
@JohnSenior I should attempt a new topic sometime soon. I haven't really ventured out of bounds for a while.
@KannappanSampath: Howdy!
 
@robjohn I think it is a good idea to venture a bit wider sometimes
 
Hi @JohnSenior and @robjohn
I came in here a few minutes ago, it was VERY quiet. :(
 
@KannappanSampath It has got a bit less quiet recently :)
(probably due to me talking rubbish ...)
 
I made all my Group Theory answers CW some time ago... I am happy that I don't have to track some stupid downvotes.
@JohnSenior That's not true! =)
 
I recently bought a book on class field theory - and one of the authors is called "Kato" ...
 
6:14 PM
Certainly not Mao Kato.
 
@KannappanSampath I guess not :)
but "our" Kato has asked some questions quite similar to stuff in my book
 
Well, I hope it's taken the way it's intended; not serious.
 
@KannappanSampath Of course :)
 
Well, polynomial rings are so awesome.
 
Not sure I would call them awesome - maybe "interesting" or "useful"
 
6:27 PM
For one, what you can do with integers, you can do with polynomials. For another, you CAN prove FLT for any reasonable polynomial ring while for $\mathbb Z$, it took Wiles to do it. :)
 
@KannappanSampath yes - that certainly makes them interesting
 
@JohnSenior, how are you doing?
:)
 
@Steenrod Hi - not so bad, thanks - and you?
 
@JohnSenior,I just found out that undergraduate algebra is basically devoid of stuff mathematicians use .That means I won't learn what needs to be learnt any time soon. :(
 
@Steenrod I don't believe that is true - I am sure mathematicians use linear algebra and groups rather a lot
(for example)
 
6:32 PM
Some books are using category theory.I came to know I would have to learn everything again in grad schoolBut I doubt if there are any tough, but self-contained detailed treatments of abstract algebra necessary for algebraic NT or algebraic geometry which are accessible to me.
 
same with fields, although I am not sure how much field theory is done by undergrads these days - I was an undergrad a long time ago
 
@Steenrod Far from true, as John puts it. For one, what one learns as an undergraduate is a basic asset in the Mathematical Journey.
@Steenrod Well, perhaps, Ireland and Rosen is accessible while I myself have not worked through it to assert it with great amount of certainty.
@JohnSenior I'd be taught about fields through this and next semester.
 
@KannappanSampath You are an undergrad already?
 
I mean accessing books like Neukirch(I saw some reviews stating it is the book) and Hartshorne.What are the pre-requisites for accessing them?
 
@Steenrod which year of studies are you in?
 
6:36 PM
@JohnSenior Hmm, yes, I am an undergraduate. :(
 
@KannappanSampath sorry - I was supposed to be asking @Steenrod :)
 
@JohnSenior, in high school.:D(That explains my over-enthusiasm)
 
@Steenrod If you are in high school, I wouldn't be worrying about Neukirch and Hartshorne yet - but ought to be concentrating on covering a wide range of undergrad subjects first
 
I am quite weird.
 
@John should be able to assist you, @Steenrod with books accessible to you in number theory. From me, I suggest you'd first work through Dummit and Foote and Herstein, or perhaps Artin's Algebra before worrying about Category theoretic formulation.
 
6:39 PM
@Steenrod most mathematicians are :)))
 
@JohnSenior, I just saw some amazon reviews on algebra chapter 0.
By Paulo Aluffi.Is it really self-contained as the title suggests?
 
@Steenrod I don't know - I have never seen it, sorry
 
@JohnSenior, thanks. :)
 
@KannappanSampath Interesting - is that an early version of the book?
 
6:48 PM
@JohnSenior I guess, the book that AMS has printed is more or less what's in the link.
 
I need to go and eat - back later folks
 

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