The h Bar

Mockingbird360

16:00

But, is any axiomatic definition of energy possible?

Sir Cumference

If you want rigorous definitions, go to mathematics. There does not exist a fundamental definition for concepts like mass, etc.

Mockingbird360

@SirCumference Well, quantum wave-functions have energy associated with them. But, where is motion in this case?

John Rennie

@Mockingbird360 The term energy doesn't have a single precise meaning.

Mockingbird360

@JohnRennie Have you checked the definition Lubos Motl wrote in a post (which is in the photo I posted here)? This seems to me most appropriate candidate for a rigorous definition, which uses a fundamental theorem to define energy!

John Rennie

Well, I suppose you can define it as the conserved quantity associated with time shift symmetry, but that's usually not a useful definition ...

Mockingbird360

16:05

@JohnRennie Why do you think it's not useful?

John Rennie

@Mockingbird360 ah, that's what Motl is referring to in his answr.

@Mockingbird360 it's a bit abstract.

dmckee

@Qmechanic I think it is arguable that kinetic theory is a sub-set of statistical mechanics, but by historical development and as taught it is usually treated as separate.

Mockingbird360

But, it's more fundamental.

dmckee

I'd prefer not to seem them combined, but in a low-key, easy-going kinda way.

John Rennie

@Mockingbird360 Unless you understand Langrangian mechanics that definition is utterly opaque!

Akash. B

16:08

Hi

dmckee

I even teach a limited version of kinetic theory in my intro-classes, because I think it is the most accessible really ``beautiful'' result in physics.

Mockingbird360

@JohnRennie Yeah, but it's still more fundamental. And it's not like we can't get to the more familiar versions from this fundamental one.

Secret

what's the symmetry associated with the local conservation of 4-momentum?

bolbteppa

energy and momentum are not separate

John Rennie

@Mockingbird360 Fundamental is not necessarily equal to useful

2

Akash. B

16:11

Come on guys try to support my dream, May be something I can do about the world end

Secret

@bolbteppa but isn't 4-momentum already contain energy as its zeroth term?

bolbteppa

4-momentum is the conserved quantity as a result of a system with space-time translational symmetry, according to modern physics in Noether's theorem, all non-conserved forces are said to be the result of unaccounted for degrees of freedom and hence approximations

Secret

right. makes sense

bolbteppa

Yeah, but $E^2 - p^2 = m^2$, they are not independent

Akash. B

Come on teach me ,The world will know you through me

Secret

16:13

ok I see

Akash. B

Come on I am going impatient

Mockingbird360

Yeah, that's right. @JohnRennie But, the definition in classical mechanics uses circular reasoning,

Akash. B

Anyone?

bolbteppa

My understanding is that kinetics is just multi-particle quantum mechanics with a time-dependent Hamiltonian, with such high numbers of particles that you can't use ordinary QM tools, and so has not even been fully properly formulated as a theory yet, relying a lot on classical approximations, while standard statistical mechanics is multi-particle QM with a time-independent Hamiltonian, again with such high numbers of particles you can't use ordinary QM directly you need to use averages

Akash. B

Why words are so special ?

bolbteppa

16:18

It's too hard to really get into, such a backlog of stuff leading up to it :p

Akash. B

Guys please, please

Mockingbird360

@Akash.B I don't get why are you so desperate and about what?

Akash. B

The world is gonna end, come on do something

Master Yushi

You can't stop the entropy increase

Secret

(this discussion is really strange)

Akash. B

16:21

joules per kelvin?

Entropy?

Balarka Sen

I am internally dying while reading these messages.

John Rennie

Who flagged Akash's comment about the world ending? How on Earth can that be construed as seriously offensive?

Akash. B

What is the need of that ? Why you star as interesting ?

John Rennie

You do realise that frivolous flagging will earn you a ban?

Semiclassical

@JohnRennie b/c knee jerk flags

Secret

16:24

Balarka: It's really strange, I cannot make sense of his messages

nitsua60

@Akash.B your inputs largely aren't germane to the physics-directed topics being discussed. And now you're drawing flags, presumably because people don't particularly enjoy your contribution. (It would be helpful if those people used their words, of course.)

Master Yushi

@BalarkaSen Everyone is, regardless of reading this or not

Semiclassical

I’m sorta resigned to how abused the spam flags are

Akash. B

Okay I am sorry

nitsua60

If you want to converse go ahead and join the conversation. But trying repeatedly to bring the conversation around to your personal drama doesn't seem welcome.

Balarka Sen

16:25

A part of my heart blackens and rots and decomposes inside my ribcage everytime I read these messages

hbar is unhealthy for me

John Rennie

Anyway, the world is going to end. Just ... not for a while :-)

At least, I hope not.

Secret

@BalarkaSen you should cleanse yoursef with some death grips

Akash. B

I won't do it again

nitsua60

@Semiclassical It really seems to me that room-regulars need to be speaking up more.

Secret

I highly suggest that as a remedy for strangeness

nitsua60

16:26

Gently and patiently and in a generally Be Nice way, but go ahead and speak up, people.

Akash. B

okay

Balarka Sen

@Secret Fun fact: Death Grips is collaborating with the guy who directed Shrek

Secret

eh?

Balarka Sen

I'm not joking, like, seriously

Look it up

Secret

hmm...

John Rennie

16:27

Anyone who abuses the flagging system will be forced to learn relativistic hydrodynamics. Or if that's considered too inhumane we could just roast them alive instead ...

Balarka Sen

I'm worried about the future of music

Meanwhile, this is pretty good:

Aesop Rock - None Shall Pass (Official Lyrics)

►

Semiclassical

@nitsua60 I don’t see how that helps. Flags are anonymous as far as the regular users know

Master Yushi

Vidya Vox

is the future

Balarka Sen

@MasterYushi Oh jesus flubberducking god

Master Yushi

xD

Akash. B

16:29

anyone

Semiclassical

Peer pressure doesn’t help much in that setting

nitsua60

@Semiclassical You don't see how a culture of speaking up when unwanted chat pops up before flagging would be helpful? I can't prove it to you, I can just testify that I've witnessed it.

John Rennie

@Akash.B the world isn't going to end in six years. Please stop going on about it.

nitsua60

A healthy room is one, in my opinion, in which people feel welcome (and even encouraged) to actually say what's bothering them, trust that tehy'll be heard, and people come to vague consensus.

Secret

arxiv.org/abs/gr-qc/0603009

As far I knew, a relativistic fluid is just going to punch through literally anything

Captain Bohemian

16:31

@bolbteppa a system with time-dependent Hamiltonian refer to a non-equilibrium physical system? So kinetics is to describe a non-equilibrium physical system? is it an interacting system?

Akash. B

But ,Stephen Hawking

John Rennie

@Secret :: scream ::

Semiclassical

This assumes that the flaggers are active participating members of the room

user4704

If a user is posting a bunch of strange and nonsensical messages, talking to them, asking them to stop or clarify or whatever, is probably better as a first step then calling in what is effectively an artillery strike on them.

John Rennie

@Akash.B Stephen Hawking didn't say the world is going to end in six years.

nitsua60

16:32

@Akash.B You've been asked nicely, then you've been told by the room owner. Now I'm kicking you out of the room for a short time.

Semiclassical

And I’m dubious of thst. I feel like there’s a lot of drive-by flagging

user4704

That is what appears to have happened here, so far as I can tell, and it's particularly questionable given nitsua60's starred message over there.

Balarka Sen

@JoshPetrie Squids eating dough in a polyethylene bag are fast and bulbous

I can't go back to your prowling land

nitsua60

@Akash.B when you come back please feel free to talk in a coherent way about a notable physicist. "But Stephen Hawking" doesn't count as a useful contribution to dialogue. "But Stephen Hawking wrote X paper in which he predicted the Milky Way's central SMBH would expand drastically in the year 2020" with a link would be useful, for instance.

user4704

@Semiclassical Dubious of what? I would agree that there's probably a lot of drive-by flagging going on, yes.

Balarka Sen

16:34

And also, bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawnto‌ohoohoordenenthurnuk

bolbteppa

@CaptainBohemian yes

Akash. B

I just told what I have read

John Rennie

@BalarkaSen that famous Finnish prog rock band

Akash. B

And I won't do it again

nitsua60

@Semiclassical You can be dubious. I'm telling you, from experience in the SE network, that it's perfectly common for what I'm calling a "healthy" room to exist, and they tend to have the quality I described.

Semiclassical

16:35

Hmm.

John Rennie

Let's not get too carried away. There was one, single, rogue flag. That is not the end of the world.

Akash. B

Okay I understand

bolbteppa

When you have large numbers of particles, you can't just set up the equations of motion for each particle separately, for example if you tried to treat the collection of particles as a stationary state problem, the more and more particles you add, the smaller the distance between distinct energy levels is, but what happens when they get within $\hbar$ distance between one another? Multi-particle QM suffers inherent quantum problems that force statistical thinking into the mix by design

Side note, JBP freaking out in a totally non-fascist way twitter.com/jordanbpeterson/status/975941537619107840

Akash. B

Now I realize, why people used to avoid me

John Rennie

@Akash.B if you can say where you read the story about Hawking, and provide a link to the article, then we can have a look at it.

Akash. B

16:39

Okay I will try for it

nitsua60

Can I just say: when I respond to a flag I expect to see either a one-line drive-by profanity-laced line from a rando that got insta-flagged by a dozen people or something flagged after a conversation in which people have been asking someone to stop, then asking again, then telling them to please stop, then summoning ROs/mods to tell them to stop... The times I've come here it's been neither.

Secret

DON'T PANIC: it's only Finnegans Wake - thunderword #1

►

John Rennie

But it's not much use to just tell us that Stephen Hawking says the world will end. How are we supposed to make any useful comment on that without full information of what Hawking is actually supposed to have said?

Secret

Balarka and JohnRennie

bolbteppa

Hawking wants us to go to other planets

Master Yushi

16:41

So does Elon

bolbteppa

Hawking, Musk etc... want it as protection from what the 25% or so of each countries authoritarian population will lead us to if we are not careful, as a precaautionary measure

John Rennie

@nitsua60 it's only the last week that the rogue flagging has broken out. In general the room is pretty well behaved.

Akash. B

english.manoramaonline.com/news/world/2017/05/03/…

John Rennie

That's 100 years not 6 years! :-)

bolbteppa

I haven't studied game theory, but I'd say a lot of this comes down to game theory

nitsua60

16:42

@JohnRennie I agree that recently (say, months) it's been pretty good excepting the last few days. On the other hand, the reason I have the room starred is because of its notoriety as a hotspot within the chatosphere.

Akash. B

Well A life span of human being

John Rennie

And the world isn't going to end, the world will do just fine. It's the primates infesting it that are going to have problems :-)

Akash. B

Is that a rumour?

John Rennie

@Akash.B is what a rumour?

nitsua60

@Akash.B It would be courteous to use your words rather than dropping naked links. Something like "Stephen Hawking says we need to be off-Earth in a sustainable way within 100 years, see here [link]" makes it easy for people to converse with you without having to go do homework if they don't want.

Akash. B

16:45

Okay thank you for your suggestion

nitsua60

Crap. s/says/said up there. I guess it hasn't really sunk in for me yet =\

Akash. B

How did Stephen Hawking predict it?

nitsua60

Alright, everyone--kids have an early dismissal because of a huge snow we're supposed to get so I gotta run. Be well!

Secret

good luck on the kids

Akash. B

well I am not a kid I am a teen

hmm

Is that inappropriate?

Balarka Sen

16:48

sigh

I think I am more or less 90% dead inside now

Akash. B

I am sorry

I apologize

hello

anyone?

Please forgive me

Sid

@Akash.B You shan't be forgiven. :P

Akash. B

I have done a mistake

Abcd

@Akash.B Control

Akash. B

What?

Sid

16:54

...No one's calling you a kid. sigh

Tanuj

I'm seriously hoping for a rule on SE that allows mods to block someone over excessive guilty pleading and forgiving

Secret

h bar is really strange recently and I still don't understand how to deal with strangeness, for it is a whole new level over weirdness we all familar with

John Rennie

@Akash.B when nitsua60 said kids he was referring to his own children.

Akash. B

I won't do it again

Master Yushi

oh god

Tanuj

16:57

@Secret He/she has definetly trumped you over the strangeness and weirdness part.

Secret

I think I might need one up quark and one down quark into h bar so that it gets neutralised into a $\Lambda$ baryon :P

Tanuj

What's even his problem ? Did he receive some sorta ban or what ?

Abcd

@Tanuj Akash's ?

Akash. B

Okay I am leaving bye

nitsua60

@Tanuj Mods can block anyone for anything. I claim it'd be more helpful if people in the room said "hey, this. This we want you to stop. Here's why...." Then bans can come, after words have proven insufficient.

Abcd

16:58

Banned people can't speak for 30 minutes

John Rennie

More inappropriate flagging! We need the mods to look into who is raising those flags.

Tanuj

ywa

Secret

@Tanuj No worries, The Labs are now investigating this new phenomenon of strangeness. We will soon figure out how to deal with it

:P

Abcd

@JohnRennie Which message was flagged?

If it was Akash's then I think it was flagged as " spam"

Sid

I am not sure, mods are at liberty to say what was flagged...

John Rennie

16:59

3 mins ago, by Tanuj

I'm seriously hoping for a rule on SE that allows mods to block someone over excessive guilty pleading and forgiving

Tanuj

@nitsua60 just do whatever possible to make this room a bit more stable and less nonsensical

Abcd

Who would flag that!?

John Rennie

Someone who seriously misunderstands how the flagging system works

Secret

that's nothing inapproporitate in that message

Semiclassical

A reminder to everyone that there is the option of hiding a given users posts

nitsua60

17:00

@Tanuj It can't be me. It's got to be the regulars and ROs and local mods, first and foremost.

Tanuj

hmm , looks like "he's" gone . Back to normal working again.

Abcd

@Secret maybe he found it referring to him

Secret

well, only the mods will knew anyway...

nitsua60

@Tanuj Let me be clear: in my experience it'd be a lot more helpful if you'd said to Akash "excessive pleading and apologizing is obnoxious, it takes up space and makes it clear that you think everything's about you when it's not, please stop" rather than making an oblique comment.

user4704

:|

nitsua60

17:01

@JohnRennie that's ^^ not terribly helpful, either.

Tanuj

@nitsua60 I thought he was spamming and wasn't gonna listen .

ACuriousMind

@Abcd That's not spam. Spam is for overt self-promotion or posting random links. If something is not spam in that sense nor blatantly offensive, please either use your words to tell everyone what you're uncomfortable with, or, if you do not feel comfortable speaking publicly, raise a custom mod flag.

Secret

too many mods in one spot = doomsday is coming

John Rennie

Sorry, an attempt at levity ...

Akash. B

Sorry for once again

ArtOfCode

17:02

Please stappit with the nonsense flags, folks... they really don't endear the room to people.

Akash. B

It was me

Tanuj

@Akash.B Please stop !

John Rennie

There must be a system for finding out who is doing the flagging.

Abcd

@ACuriousMind what is a mod flag?

John Rennie

Can't the community mods help?

nitsua60

17:03

Hang on, I'm freezing the room for a sec. There's too much going on.

Akash. B

Come on you have found the suspect

user4704

@Abcd Under the "flag as spam/offensive" option should be a "flag for moderator" option.

Feeds

nitsua60 has frozen this room.

nitsua60

@Akash.B Stop with the short and incoherent messages. Put together a complete thought and make clear to whom you're addressing it. These little bursts interrupt others' conversation.
Yes, there's a way flaggers can be identified. But only if a local elected moderator is in the room at the time. Check Meta.SE for details if you're interested. Yes, the community managers can help.
But I'd say that when the room's at the point where flags are flying and speculation's abounding and you want to call in a CM... that's waaaaay too far afield of chat's purpose (supporting SE), and it's been way too…

Flaggers: use your words first!

6

Feeds

nitsua60 has unfrozen this room.

Balarka Sen

17:04

Some words

More words

That escalated quickly

Tanuj

few words

nitsua60

@Akash.B Drop it. I don't care. You flagged something and now realize better. Great. It's done.

Akash. B

Yes I did it

nitsua60

@Akash.B I told you to drop it, now I'm kicking you from the room for a little bit.

Tanuj

lol !

Sid

17:06

@Akash.B No one cares anymore pal. Just let it go.

Tanuj

@nitsua60 Thank you ! You saved h bar

nitsua60

@BalarkaSen @Tanuj if those are attempts at levity they're not great in timing.

Tanuj

@nitsua60 I certainly did not intend levity.

nitsua60

@Tanuj What did you intend?

Balarka Sen

@nitsua60 You're simultaneously asking us to drop the concurrent topic of conversation about flags and prohibiting us from moving on.

I can try to pose some math if levity is not well-recieved

ArtOfCode

17:09

Bonus points for mathematical levity

Balarka Sen

I tried that yesterday, it got me kicked :P

Tanuj

@nitsua60 telling them to use "a few words" , if they don't want to speak about it at length , its okay , but atleast use a few words is what I was saying

Balarka Sen

(It was a joke about suspensions and the operation of "reduced suspension" in topology)

nitsua60

@BalarkaSen I don't intend to be asking you to drop the topic of how rooms run well. If we're speculating about who flagged what then it's pointless and tends (in my experience) only to lead to more drama.

@BalarkaSen Yes, for which I'll apologize again. I'm sorry again for the mis-read and the reaction.

Tanuj

@nitsua60 I guess you need to chill , it's all good

Rand al'Thor

17:11

@ArtOfCode Why did the mathematician name his dog Cauchy? Because it left a residue at every pole.

nitsua60

@Tanuj Thanks.

Balarka Sen

@Randal'Thor Hey! How's it going

ArtOfCode

@Randal'Thor ...I'm not required to actually get these jokes, am I?

Rand al'Thor

Oh hey @Balarka! Long time no see.

Balarka Sen

@nitsua60 I wasn't being accusatory, it's pretty natural the confusion occured

John Rennie

17:12

@ArtOfCode it's a complex joke :-)

Tanuj

Yea ! "The h Bar" is back ! :)

Rand al'Thor

@ArtOfCode Hopefully the physicists will ;-)

nitsua60

@Tanuj I get that, though I'll say that the reception that some of my messages have gotten (star board) seems to indicate that not everyone here's on the same page on what's good and bad to have going on.

ArtOfCode

@JohnRennie I get the feeling that this is more wit going straight over my head...

Balarka Sen

@Randal'Thor There's also a relevant one about all the poles being on a certain localized area of Europe

So if you integrate over a loop around that you'll get something nonzero

@ArtOfCode You asked for it!!

Tanuj

17:13

@nitsua60 hmm there has to be a set of well defined rules as to what is good or bad , unless there are any rules , I don't see everyone being on the same page , that's where SE needs to improve.

nitsua60

@BalarkaSen And it's one of those where I remember mousing back and forth five or six times thinking "should I?" Which is an obvious sign that I actually should have taken my own advice and said "Hey, please stop discussion suspensions!" (At which point six people would have pointed out how I missed the joke.)

Balarka Sen

LOL

Sorry for that one.

Rand al'Thor

@BalarkaSen What's the value of a contour integral around western Europe? Zero, of course.

Balarka Sen

Ah yes

That is indeed the one

nitsua60

@Tanuj There can't be and won't be. It's too-complex a system to codify like that. What there can be is a practice where people are in the habit of actually saying "I think this is bad" or "I think this is good." I don't see that happening much here. And maybe it's self-directed narcissistic confirmation bias, but the stars at right tell me that it needs to be talked about more.

Rand al'Thor

17:15

@ArtOfCode How do Frenchmen do Fourier analysis at the seaside? Using Laplage transforms.

ba dum tish

nitsua60

(Either in the room or on meta, I don't know.)

ArtOfCode

@Randal'Thor \o/ one I actually get

Tanuj

@nitsua60 yup , seriously needs a discussion.

nitsua60

Aaaaand... now the kids are home. I've ignored my work responsibilities long enough, now let's go half-ass my family responsibilities. Be well, all!

@Akash.B Peace.

Sid

@Tanuj Just drop it pal.

John Rennie

17:16

Let it go.

Tanuj

@Akash.B peace.

John Rennie

→ 2 messages moved to trash

Balarka Sen

Maybe not the best move.

Tanuj

@JohnRennie so did your edm taste develop ? Now don't flag this for off topic :p

John Rennie

EDM is one of those secret vices I'm vaguely ashamed of :-)

Tanuj

17:19

your guilty pleasure ?

Anonymous

@JohnRennie Any idea how to share Jupyter notebooks, by mail? I got a .ipynb on my PC and I need to send it someone. Not sure if just sending the raw file will do (because I normally need to open it from the Anaconda Prompt)

Anonymous

Can I create a online version of it?

John Rennie

I think a Jupyter notebook is like an Excel file or Word document. It's not a program itself - you need the appropriate Python addons to pen it.

Anonymous

I've seen people sharing links to Jupyter notebooks, online, but I'm not sure how to do that

Tanuj

@PrathyushPoduval Hey pal !

Prathyush Poduval

17:21

Hey!

Tanuj

@PrathyushPoduval need some help

Prathyush Poduval

Howz it going?

yeah go on

Tanuj

Prathyush Poduval

Whoah was this room frozen?

John Rennie

@Blue presumably the notebook is on a web server somewhere ...

Prathyush Poduval

17:22

Damn I missed the fun

Anonymous

@PrathyushPoduval I just noticed :P

Prathyush Poduval

what happened?

Tanuj

what was the condition of infinite solutions for two variables ? I remember that for 3 variables but just forgot what it was for 2 variables.

Prathyush Poduval

It's just matrices

you can write it as a matrix equation

Lemme see how to write matrices in latex....

@Tanuj [{k+1,8},{k,k+3}][{x}{y}]=[{4k}{3k-1}]

John Rennie

Isn't it just th determinant of the matrix being zero?

Tanuj

17:24

@PrathyushPoduval okay.

@PrathyushPoduval ah , a 2x2 matrix

Prathyush Poduval

@JohnRennie Yes it is

John Rennie

i.e. $(k+1)(k+3) - 8k = 0$

Prathyush Poduval

@Tanuj Yeah, I've written it as a matrix equation, hope you can understand it :P

Anonymous

@JohnRennie Thanks. But I'm not sure how to share a link to that. I'm asking in the Python chat on SO, let's see

Sid

@JohnRennie yeah.

That would probably mean 2 values of k.(Unless of course, they are trying to be too clever)

Tanuj

17:25

@PrathyushPoduval didn't get what you did after writing the matrix of coefficients of x and y

John Rennie

@Tanuj do you know how to use matrices to solve simultaneous equations?

Prathyush Poduval

@Tanuj Now, if the matrix [{k+1,8},{k,k+3}] was invertible, then you can multiply by the inverse and solve the equation

so the condition is the matrix must not be invertible

Tanuj

@JohnRennie I'm afraid not , no

Prathyush Poduval

that is, the determinant of the matrix should be 0

John Rennie

@Tanuj ah, in that case we won't be making much sense to you ...

Tanuj

17:27

yea

So , for ininite solutions , just do determinant of matrix of coefficients of x and y = 0?

John Rennie

Suppose you have simultaneous equations:
ax + by = c
dx + ey = f

Tanuj

yea

John Rennie

To find x replace the x column, with the column to the right of the equals to get (erm - John tries to remember the MathJax syntax)

$$ \begin{matrix} c && b \\ f && e \end{matrix} $$

It worked! :-)

Tanuj

ok

Master Yushi

How do I make mathjax render?

Tanuj

17:31

solving that and putting that equal to 0 gives me values of x ?

Prathyush Poduval

@MasterYushi the bookmark

John Rennie

Now take the determinant of the matrix i.e. $ce - bf$

Prathyush Poduval

@MasterYushi math.ucla.edu/~robjohn/math/mathjax.html

John Rennie

Now take the matrix formed from the coefficients of x and y: $$ \begin{matrix} a && b \\ d && e \end{matrix} $$

Tanuj

@JohnRennie yea

Master Yushi

17:32

Thanks

Tanuj

@JohnRennie ok

John Rennie

And take the determinant of that: $ae - bd $

Tanuj

@JohnRennie yea

Master Yushi

Do i have to click it everytime to update the page?

John Rennie

And just divide one by the other $$ \frac{ce - bf}{ae - bd} $$ ad that's the $x$

Prathyush Poduval

17:34

@MasterYushi No, once you click it it keeps updating automatically

Tanuj

@JohnRennie woah , okay. Why was I never taught that !

Prathyush Poduval

@Tanuj Which class are you in?

Tanuj

@JohnRennie so how does doing all that relate to my question

@PrathyushPoduval 12th pass

Master Yushi

Had to refresh the page, it is working now

John Rennie

@Tanuj suppose $ae - bd = 0$ then you are dividing by zero.

Prathyush Poduval

17:35

@Tanuj It should be there in the syllabus right?

Matrix method of solving

equations

Tanuj

@PrathyushPoduval its not . Or maybe it would be but I was never taught

Prathyush Poduval

Which board?

Tanuj

CBSE

@JohnRennie yea

Prathyush Poduval

It's defenitely there in CBSE

Master Yushi

It is in ISC and ICSE

John Rennie

17:36

@Tanuj When you find you are dividing by zero it means there are infinitely many solutions.

That's why when the question asks what the criteria are for infinitely many solutions we just need to set the determinant of the matrix to zero and solve for $k$

Prathyush Poduval

@Tanuj ncert.nic.in/textbook/textbook.htm?lemh1=4-6

example 27

@JohnRennie doesn't infinitely many solution have additional conditions too?

adj(A)*Y=0 (or something like that i think, I've never looked into that properly)

John Rennie

@PrathyushPoduval I can't remember I'm afraid. I last did this forty years ago :-)

Tanuj

Nah , I'm sure there isn't .

Sid

@JohnRennie *years

Master Yushi

There is this assertion and reasoning question, which simplifies down to:

Statement 1- Angle1 = Angle2, because c1 and c2 and proportional
Statement 2- Angle1 = Angle2 for all c1 and c2

Now, given that statement 2 is correct, do you think it is the correct explanation for statement 1 or not?

Tanuj

17:41

@PrathyushPoduval Okay , but that is seriously different from what @JohnRennie was saying.

Sid

@MasterYushi Um... Statement 2 doesn't give any explanation at all.. :/

Master Yushi

That's what i chose as the answer, that both statements are correct but s2 is not the correct explanation for s1, but apparently the answer is just the opposite lol

Prathyush Poduval

@MasterYushi are you asking if statement 1 is the cause of 2?

sorry internet temporarily lost connection

@Tanuj Actually, That's exactly what he was saying

Sid

@PrathyushPoduval what I understood is that they are saying statement 2 is the reason for statement 1. Which makes precisely zero sense.

Prathyush Poduval

exactly

Tanuj

17:43

@PrathyushPoduval but it didn't appear like that to me.

Master Yushi

Quoting the question : (A) Both statements are true and s2 is the correct explanation for s1

(B) Both statements are true but s2 is not the correct explanation for s1

Sid

@MasterYushi And they say (A) is correct?

Master Yushi

yes

haha

Prathyush Poduval

@Tanuj So, JR was showing that the solution was =$\frac{[\begin{matrix} e && -b \\ -d && a \end{matrix}][\begin{matrix}c\\f\end{matrix}]}{det}$

Curio

Why do London forces change because of the dimension of the molecule?

Prathyush Poduval

17:46

where det is the determinant

Master Yushi

I will just post the full question if anyone wants to see

Prathyush Poduval

yeah do it

Tanuj

yes

Master Yushi

Q.77

Both sets of lines are parallel with respect to each other so the angle between them won't change

Tanuj

guys ,

what are your thoughts on this ? I know clockwise rotation would yield a negative sign , but how do I decide about which line is the point being reflected /

Master Yushi

17:52

(A) i think

Prathyush Poduval

@MasterYushi A

Tanuj

lol definitely not

Sid

@MasterYushi To me, those two options seem contradictory. For instance, if it is true for all c2 and c3 then, c2 and c3 need not be proportional...

Prathyush Poduval

statement 1 is correct because statement 2 is

but it is not an iff condition

Master Yushi

@Tanuj It is just another point on the same unit circle

Tanuj

17:53

@MasterYushi nope , just check.

Sid

@PrathyushPoduval Ah, yeah. that is probably true and the correct interpretation..

Master Yushi

@Tanuj I am pretty sure

Tanuj

@MasterYushi I told you its wrong

Prathyush Poduval

@Tanuj D

Tanuj

just draw it out

@PrathyushPoduval yea , teach me how ! :p

Prathyush Poduval

17:55

Damn, I'm very much out of practice with jee, I think i'll just skip it lol

@Tanuj Drawing the vector figures

vec P makes an angle $\theta$

vec Q makes an angle $\alpha-\theta$

the angle bisector of P and Q makes an angle $\frac{\theta+\alpha-\theta}{2}=\frac{\alpha}{2}$

Tanuj

@PrathyushPoduval how do I know where alpha-theta would lie

@PrathyushPoduval when did you give JEE ?

Prathyush Poduval

I'm (hopefully) giving it this year

with 0 prep

Tanuj

okay

Prathyush Poduval

@Tanuj Q either lies to the left or right of P, for both cases what I gave holds

Tanuj

@PrathyushPoduval cool , got it. Thanks

Transcript for