you can just do basic arithmetic on the integers as an additive group, just teach your kids group theory ;-)
― flopson, Wednesday, 11 December 2013 02:19 (ten years ago) link
for division i guess you either need a euclidean ring or a fullblown division ring, in which case division is just multiplication by inverses
― flopson, Wednesday, 11 December 2013 02:23 (ten years ago) link
If you believe -1 x a is -a, then -1 x -1 is -(-1), and negative negative 1 is plainly 1.
But once you believe -1 x -1 = 1, I think you believe that a negative times a negative is a positive in general.
― Guayaquil (eephus!), Wednesday, 11 December 2013 02:36 (ten years ago) link
elegant
― the late great, Wednesday, 11 December 2013 03:20 (ten years ago) link
we had to prove all this bullshit in my first real analysis class, to give the impression of "rigour"--but we didn't even construct the real numbers (using dedekind cuts, etc), just stated the Completeness property as an axium--such a waste of time
― flopson, Wednesday, 11 December 2013 03:27 (ten years ago) link
Think it might be useful to think of multiplication as making a copy or n copies of something to replace the thing and multiplication by -1 as making an inverted copy. So say you have a white disk than multiplying by -1 you replace it with a black disk and vice versa, or better yet you have an Othello token and just flip it over.
― The Glam Of That All The Way From Memphis Man! (James Redd and the Blecchs), Wednesday, 11 December 2013 03:42 (ten years ago) link
is this thread a boys club? where the math ladeez at?
― the late great, Wednesday, 11 December 2013 03:59 (ten years ago) link
iirc harbl studied math but she said she has forgotten all of it and left it all behind and is a lawyer now
― flopson, Wednesday, 11 December 2013 04:00 (ten years ago) link
kid i was tutoring deferred his exam :-\
― flopson, Wednesday, 11 December 2013 04:06 (ten years ago) link
why negative times negative is positive
I feel like I did something like this in discrete math, you start with basic definitions of integers and parity or w/e and then do a formal proof or w/e?
― ☞ (brimstead), Wednesday, 11 December 2013 04:16 (ten years ago) link
lol n/m i'm drunk and listening to bill withers
― do a formal proof or w/e (brimstead), Wednesday, 11 December 2013 04:18 (ten years ago) link
how do i shot basic simplification of roots
http://farm8.staticflickr.com/7335/11318231686_aee01101ef_b.jpg
― the late great, Wednesday, 11 December 2013 04:25 (ten years ago) link
You're asking seriously?
― The Glam Of That All The Way From Memphis Man! (James Redd and the Blecchs), Wednesday, 11 December 2013 04:31 (ten years ago) link
Oh, I see you are making fun of the person who put the question marks.
― The Glam Of That All The Way From Memphis Man! (James Redd and the Blecchs), Wednesday, 11 December 2013 04:47 (ten years ago) link
no i'm asking seriously :((((
― the late great, Wednesday, 11 December 2013 05:51 (ten years ago) link
defeated by precalc ;_;
― the late great, Wednesday, 11 December 2013 05:53 (ten years ago) link
Multiply by conjugate?
― do a formal proof or w/e (brimstead), Wednesday, 11 December 2013 05:59 (ten years ago) link
rotation of axes??
― do a formal proof or w/e (brimstead), Wednesday, 11 December 2013 06:00 (ten years ago) link
last step looks like some bullshit, no? rationalize the denominator, b then u got sqrt(1 + 2/3sqrt(2)) not sure how much more u can smiplify tho?
― flopson, Wednesday, 11 December 2013 06:00 (ten years ago) link
it works on a calculator
― the late great, Wednesday, 11 December 2013 06:07 (ten years ago) link
google it!
sqrt((2+sqrt(2)) / (2 - sqrt(2)))-sqrt(2)
― the late great, Wednesday, 11 December 2013 06:11 (ten years ago) link
ok got it
― the late great, Wednesday, 11 December 2013 06:41 (ten years ago) link
Interesting post on zero indexing:
http://exple.tive.org/blarg/2013/10/22/citation-needed/
Author interviewed Martin Richards, author of BCPL and the supposed originator of zero indexing. Conclusion: it was a stylistic decision (i.e. it wasn’t commentary on zero’s inclusion in ℕ or whatever).
― Allen (etaeoe), Wednesday, 11 December 2013 15:00 (ten years ago) link
interesting to think about how stylistic concerns can be aligned naturally with mathematical principles (vs when they're not aligned). makes me think about what style really means and stuff.
― do a formal proof or w/e (brimstead), Thursday, 12 December 2013 03:07 (ten years ago) link
0 is so not a natural number
― flopson, Thursday, 12 December 2013 03:43 (ten years ago) link
mathematical principles are always about style
― lollercoaster of rove (s.clover), Thursday, 12 December 2013 04:31 (ten years ago) link
I once gave this answer but in a much wordier way on this thread:
http://math.stackexchange.com/questions/9933/why-negative-times-negative-positive
― o. nate, Thursday, 12 December 2013 15:50 (ten years ago) link
considering prepping a talk for an undergrad conference in january, anyone got any topics to suggest?
― flopson, Sunday, 15 December 2013 03:26 (ten years ago) link
https://www.simonsfoundation.org/quanta/20121002-getting-into-shapes-from-hyperbolic-geometry-to-cube-complexes-and-back/
great article on the classification of 3-manifolds, written at an extremely accessible level. basically this guy thurston conjectured 23 theorems that, once all proven, would result in classification. my topo prof proved a result that was used to prove the last three conjectures in one sweep, and article goes in some detail into his research. super interesting stuff, to me at least
― flopson, Sunday, 15 December 2013 03:40 (ten years ago) link
thanks for the link -- that's very clear!
― lollercoaster of rove (s.clover), Sunday, 15 December 2013 05:21 (ten years ago) link
Yeah
― The Glam Of That All The Way From Memphis Man! (James Redd and the Blecchs), Sunday, 15 December 2013 05:23 (ten years ago) link
it would be an interesting history of math to classify what programmes have led to the most research -- i suspect classification programmes themselves would probably lead the pack.
― lollercoaster of rove (s.clover), Sunday, 15 December 2013 05:24 (ten years ago) link
classification of surfaces seemed like it didn't take very long once they figured out what they were doing
― flopson, Sunday, 15 December 2013 05:32 (ten years ago) link
oh yeah, finite simple groups, too
― flopson, Sunday, 15 December 2013 05:33 (ten years ago) link
arguably, figuring out what you're doing is typically the hard part.
― lollercoaster of rove (s.clover), Sunday, 15 December 2013 05:38 (ten years ago) link
great little history of the classification of surfaces on appendix D of this book http://download.springer.com/static/pdf/997/bbm%253A978-3-642-34364-3%252F1.pdf?auth66=1387259121_9a9118105634f100257c6f624c9329f0&ext=.pdf (full pdf)
― flopson, Sunday, 15 December 2013 05:49 (ten years ago) link
gah i should be studying for my analysis exam... blegh
― flopson, Sunday, 15 December 2013 06:03 (ten years ago) link
which 2 should i take next semester out of these 4
real analysis 4 (measure theory, functional analysis)differential geometrytopics in geometry & topology course on cube c0mplexesdiscrete mathematics of paul erdos (taught by the great vasec chv4tal http://users.encs.concordia.ca/~chvatal/6621/)
― flopson, Wednesday, 18 December 2013 18:52 (ten years ago) link
real and discrete OR differential and cube complexes
― the late great, Wednesday, 18 December 2013 18:53 (ten years ago) link
i sort of hated analysis 3 but while studying for it and memorizing all those theorems i became really impressed with it and now have the urge to take the 4th. also i've heard measure theory is one of those things you've just *got* to learn and this guy would teach it properly
― flopson, Wednesday, 18 December 2013 18:53 (ten years ago) link
interesting, why those 2 diff pairings?
(xp)
― flopson, Wednesday, 18 December 2013 18:56 (ten years ago) link
i've always had better luck in school when i take courses with some connection to each other rather than courses which have different approaches
although ... is real analysis useful in differential geometry?
― the late great, Wednesday, 18 December 2013 18:57 (ten years ago) link
yes
― flopson, Wednesday, 18 December 2013 18:57 (ten years ago) link
pairing of most similar would be cubes + discrete, diff geo + ana
oh okay. that's what i'd do then.
(higher math n00b)
― the late great, Wednesday, 18 December 2013 18:58 (ten years ago) link
cube complexes was developed by algebraic topologists & geometric group theorists, people who exploit an analogy (functor or whatever) between topological spaces, infinite groups, and cayley graphs of infinite groups, to prove results in group theory & 3-manifold theory. so graph theory would come up
― flopson, Wednesday, 18 December 2013 18:59 (ten years ago) link
the simplest vers of diff geo is, like, in multivariable calculus taking a surface integral
yeah that's about as far as i got in geometry
― the late great, Wednesday, 18 December 2013 19:02 (ten years ago) link
that article i posted upthread goes into the CC stuff, with some quotes by dude who is teaching the course (and is like world champion of cube complexes)
― flopson, Wednesday, 18 December 2013 19:03 (ten years ago) link