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Page: 1 2 3 4
Comments:
<0> if A/B = A u B, how do I explain that B is not an empty group?
<1> uh?
<1> Please clarify
<2> indeed
<0> I don't know how to translate the exact words :/
<2> specify & clarify
<1> shay: what language?
<2> A,B groupd and B normal ?
<0> koro, hebrew
<1> no, that wouldn't make any sense
<1> shay: uh, then we have a problem here :)
<1> i think he meant 'set' only
<0> guessed so :)
<1> did you shay ?
<2> but why empty group then ?
<2> so A/B = A without B ?
<0> yeah
<0> empty set
<2> ah ok
<0> (just checked the plaintex simbolism in the topic)
<0> how do I explain that if A / B = A u B, then B cannot be an empty set ({})
<2> B can be the empty set though
<3> is A/B the quotient, or set difference?
<3> no group is empty anyway
<2> what's a set quotient ?
<1> shay: the usual notation is A\B
<1> it's not the same thing
<2> oh groups again - ok
<0> I see, right
<0> sorry, I'm pretty new to modern math
<2> but B can be empty i think
<0> kmh, how would you explain it?
<3> if B=empty then A\B=AuB=A
<1> A\B = A u B if and only if B is empty
<2> A \ {} = A
<1> that's what he wants to show
<2> of
<2> so must be rather than cannot
<1> so, shay, suppose B is nonempty. Let x be an element of B. If x is in A, then x is not in A\B, but since x is in A u B it cannot happen that A\B = A u B
<1> now if x is not in A, then x is not in A\B, but x is in A u B, again a contradiction
<1> thus B is empty
<3> oh... yes that does make sense
<2> hooray to koro
<0> great koro
<0> thanks
<0> I think that I'll need to learn the words in english
<1> hehe
<1> Boker tov
<2> shay : and the use of modal verbs :-P
<3> maybe look at wikipedia, if they ahve a hebrew version
<3> and then go to the english page
<1> that's all i can say in hebrew and it's probably wrong
<0> no, it's fine :)
<1> :D
<0> (if you intent to say good morning, at least)
<1> yeah
<2> shay : actually there's probably some english-hebrew math dictionary
<0> searching it
<4> The width of a rectanlge is 4 inches more than the length. The area is 45 in ^ 2. What would be the length and the width?
<4> For some reason, I can't get this. It's driving me crazy.
<3> let L and W be length and width, find some equations between L and W
<4> That's what I've been doing, I got 45 = L^2 + 4L
<4> do you think that is right?
<2> you are almost there
<3> i dont know. but solve that for L
<2> the_faulkenator : quadrtatic formula
<3> L^2+4L-45=0, factorise it
<4> I factored it and I got -2 +/ Sqrt[90]
<4> err +/1
<4> damn, i meant +/-
<3> i tihnk it factros as (L+a)(L-b) with a,b integers
<4> 11.8 is the length, I am guessing.
<4> and 15.8 is the width.
<3> you solved it incorrectly
<3> dont use the formulka, factorise the thing
<4> 9 and 5. Hurray!
<3> well they cant both be positive
<3> since ttheir product has to be -45
<4> 5 is negative, but it would have to be positive in the rectangle, right?
<3> no no
<3> the two roots are 9 and -5,
<3> so either the length is 9 or the length is -5
<3> so both values "work"---you can use the W=4+L or whatever it was to find the width, but you usually suie some out-of-band method to rule out the negative one
<3> ie "L>0 for physical reasons" or somesuch
<5> Buy my ****, bitch! https://www.cafepress.com/donkeynetshop
<6> err, catfive
<7> hi
<8> does the identity sin(a+b)=sin(a)cos(b)+cos(a)sin(b) hold for sinh also ?
<8> meaning is : sinh(a+b)=sinh(a)cosh(b)+cosh(a)sinh(b) ?
<9> What are the definitions of Sinh and Cosh ?
<9> Found it.
<9> Sinh[x] = (e^x - e^-x)/2
<8> no
<8> i dont think it will
<8> sin(a+b)=sin(a)cos(b)+cos(a)sin(b) are derived using euler's formula
<9> http://mathworld.wolfram.com/HyperbolicSine.html
<9> Cosh[x] = (E^x + E^-x)/2
<8> i know
<9> So, Sinh[a + b] = (E^(a + b) - E^(a + b))/2
<8> yes yes, i know that, thanks, but that doesnt awnswer my question really
<9> What is your question ?
<9> Ahh, made an error.
<9> Sinh[a + b] = (E^(a + b) - E^(-a - b))/2
<8> is this true : sinh(a+b)=sinh(a)cosh(b)+cosh(a)sinh(b) ?
<8> i dont think it is
<9> Sinh[a]Cosh[b] = (E^a - E^-a)(E^b + E^-b)/4
<9> Sinh[b]Cosh[a] = (E^b - E^-b)(E^a + E^-a)/4
<9> % (E^a - E^-a)(E^b + E^-b)/4 + (E^b - E^-b)(E^a + E^-a)/4 //FullSimplify
<10> Olathe: Sinh[a + b]
<9> Yep, it holds.
<8> k
<8> then coth might have multiple poles
<8> not just 0
<8> if exp(x)*exp(i*2*y)=exp(i*2*pi*k) then x=0 and y=pi*k right ?
<11> WormDrink, I think you can set x=y=0.
<8> ehrm
<8> no, thats not what i want
<8> or that doesnt awnswer any of my questions
<11> WormDrink, y=pi*k will work too.
<8> ok
<12> in my differential equations book, there is a step on a reduction of order problem where they jump from 2tv''-v'=0 to v'=ct^(1/2) saying that they are " separating the variables and solving for v' " . could someone expand this step for me?
<12> is anyone live?
<13> helloooooo
<13> hello?
<14> can anyone recommend a good book on combinatorics?
<15> ?
<16> verbose: Jackson and Goulden's Enumerative Combinatorics seems decent, though I've only had a brief look through it. I had Jackson for my combinatorics prof 3 times, and his course notes were always great.
<14> Cale: thanks
<17> I
<18> |
<17> :-) I'm reading up on sports handicapping and I have come across a sentence that I need help understanding
<18> and this is related to Mathematics in what way?
<17> "giving us a sum of .524 + .512 + .100 = 1.136, the inverse of which is .88." how is the inverse of 1.136 found to be .88? I don't get it
<17> hey, I was getting to it
<18> :)
<17> there is TONS of math in sports betting :-) that is, the smart bettors use math
<17> the idiots bet the big favorite...
<19> wub joo pipple
<13> anyone here savvy with ordinary differential equations?
<19> inverse x = 1/x
<17> Sneaky_Bastard, oh, thanks. I really should have known that by now :-)
<13> heh
<19> np
<17> it makes perfect sense now. thanks again
<19> sure 'nuff
<20> hmm heh .. I always forget how 1 / (sqr(3) / 2) = 2sqr(3) / 3 .. and etc for all similar thigns.. anyway to remember this better?
<18> DQuestions
<18> 1/sqrt(3)/2 = 2/sqrt(3) = 2sqrt(3)/sqrt(3)^2 = 2sqrt(3)/3
<20> thanks
<18> Bitte Sehr
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