AnonAccount: What is it, and what does it do? - Q&A Thread
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Russell's Paradox by Wesley Cliblingstone - Sat, 03 May 2014 17:52:43 EST ID:8PJ0nVdr No.13957 Ignore Report Reply Quick Reply
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Can any of you mathmagicians explain this paradox to me? I'm too stupid to understand the wikipedia.
3 posts omitted. Click Reply to view.
Cyril Pizzlestock - Tue, 13 May 2014 22:10:17 EST ID:iMUpn1NT No.13966 Ignore Report Quick Reply

This was a question in my friend's discrete math class. The answer is not yes and not no.
Fuck Farrystark - Fri, 16 May 2014 18:42:57 EST ID:gQ1/L8ZJ No.13973 Ignore Report Quick Reply
... There wasn't a question. And 'not no' is 'yes', yes?
Clara Mishfoot - Sat, 17 May 2014 07:08:59 EST ID:V2nhYpJ2 No.13974 Ignore Report Quick Reply
Not cyril, but I don't think "not yes" in this case would equal to no.
These interpretations are subjectively intuitive, you are free to disagree as long as you present your view:
If an answer is both yes and no, then either of them is good.
If an answer is both yes and not yes, then whatever we are inspecting does not depend in any way from our answer.
If an answer is neither yes nor no, then there is no answer and we have paradoxal situation.
Simon Buzzdock - Sat, 17 May 2014 12:46:06 EST ID:5fuPW64F No.13975 Ignore Report Quick Reply
This is dependent on the model of logic you are using
If you are just using classical two valued logic then not yes (true) equals no (false) and not no (false) equals yes (true)
but if you are using some abstract many-valued logic system with four truth values, then I guess you are free to interpret however you like
Cyril Febbleforth - Sat, 24 May 2014 13:46:10 EST ID:Fj/YvlCk No.14030 Ignore Report Quick Reply
>Not cyril, but I don't think "not yes" in this case would equal to no.

Then not yes is not no and not no is not yes?

PHYSICS, BITCH by Angus Goodbanks - Wed, 14 May 2014 16:14:56 EST ID:I2hi9ugw No.13967 Ignore Report Reply Quick Reply
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So I need to find the force of friction acting on a vehicle.
The vehicle is going 25km/h (6.94m/s) and comes to a stop
over a distance of 10m.
The mass of the car is 1250kg.
I'll lay down some formulas in the next post but this is what was stated in the question.
Angus Goodbanks - Wed, 14 May 2014 16:19:25 EST ID:I2hi9ugw No.13968 Ignore Report Quick Reply
so Ff = μFn
Fnet = Fa - Ff
W=F(parallel) Δd
p = mv (if that is worth fuckin' anything)
Ek = 1/2mv^2
Fg = mg
and in this case
Fn = mg
Angus Goodbanks - Wed, 14 May 2014 16:22:00 EST ID:I2hi9ugw No.13969 Ignore Report Quick Reply
g = 9.81m/s^2
The # I got for Fn = 12 262.5N
and I think
-Ff = Fa - Fnet
Ff = -Fa + Fnet
Shit Wondlewater - Wed, 14 May 2014 22:24:50 EST ID:dtJRvm7a No.13970 Ignore Report Quick Reply
They didn't give you the coefficient of friction, so all the equations you posted are irrelevant. The only equations you need to solve this are F = ma and the kinematic equation v_f^2 - v_i^2 = 2ad. From your problem, v_i = 6.94 m/s, v_f = 0, d = 10 m. So plugging in these values and solving for a gives you an acceleration of a = -2.41 m/s^2 (negative just means deceleration). To get the magnitude of the force of friction just multiply the magnitude of the acceleration by the mass of the car F_f = (1250 kg)(2.41 m/s^2) = 3010 N (to three sig figs).

Choice Under Uncertainty by Reuben Bollerworth - Sat, 26 Apr 2014 12:26:50 EST ID:W+YT9wqY No.13942 Ignore Report Reply Quick Reply
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Hi! I just had an Economics exam some days ago and I didnt know how to answer something:

John eats apples and carrots. His preferences are represented by
U(a,c) = f(a) * f(c) where f is strictly increasing

He can buy apples and oranges at (pa,pc) which are random variables that can take the values (3,1) or (1,3) with 50% of probability each.

Another option he has is to buy the apples and oranges before the realization of the random prices at (2,2)

Will he go for the certain option?
The thing is, I would usually try to determine if U is concave, since that would mean this guys is risk averse... I dont know how to use the fact that f is strictly increasing besides the fact that this means he always prefers more to less.
Fucking Hadgenet - Sun, 27 Apr 2014 18:39:18 EST ID:hE9drZeG No.13946 Ignore Report Quick Reply
hmm this is tough,
my intuition says he would select the (2,2) option because of diminishing marginal returns on apples or oranges. I don't think having that 3rd apple would be better than having a 2nd orange instead, but because so little info is given that can't be strictly true.

The expected number of apples and orange is 2 each (50% probability to go 3,1 or 1,3), so as you mention they are essentially complement buckets. If you assume risk aversion then one would go for 2,2 since it's a sure thing, + the marginal utility argument isn't too bad either. idk just some random thoughts
Walter Pickbanks - Sun, 27 Apr 2014 20:38:22 EST ID:W+YT9wqY No.13947 Ignore Report Quick Reply
yeah, tomorrow I will have my test.

I think maybe just had to demonstrate that the uncertain lottery can be obtained by the certain one by a mean preserving spread of the distribution fuction and then say that this implies that the uncertain one is dominated (Second Orderd Stochastic Dominance) by the first one. Then conclude that any utility maximizer individual that is risk averse would go for the certain one. The thing is, I did not see this as an option in the exam because I couldnt find a way to demonstrate that this individual is irsk averse.
Angus Pedgeberk - Mon, 28 Apr 2014 23:37:36 EST ID:3BOoYnsp No.13949 Ignore Report Quick Reply
>>13942 I have my exam. I couldnt attend the class but the professor told me that the proof goes by demostrating quasiconvexity and therefore that the random option is not Second Order Stochastically Dominated by the safe one... or something like that.

Delicious cake for anyone posting the answer before me.
Fuck Hillyson - Sat, 10 May 2014 19:18:13 EST ID:vk6kR3B3 No.13962 Ignore Report Quick Reply
>He can buy apples and oranges at (pa,pc) which are random variables that can take the values (3,1) or (1,3) with 50% of probability each.

I had a hard time trying to understand what you meant with that wording. It took me a while deciding whether pa referred to price of apple or probability of apple until I settled with price.

Due to the function U(a,c) handling both parameters a and c equally, it does not matter which is which. Therefore prices (3,1) and (1,3) yield the exact same values from function U, assuming money is a limited constant value, hence the probability of 50% you mentioned is meaningless.

We're left with two options, which involve no luck or chance. Either we settle with the value of U given by prices (2,2) or either (1,3) and (3,1).

Let us denote money by m, amount of groceries by s and pa=k, pc=n

m = ka + nc
s = a + c

Before I go on, I remind you that the apples and carrots are treated equally, there is no difference if the amount of each switch places.
Comment too long. Click here to view the full text.

volume of revolution about y-axis by Edward Pickdock - Wed, 30 Apr 2014 15:01:13 EST ID:gs0WQAqP No.13950 Ignore Report Reply Quick Reply
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sup /math/

When solving for volume of solid generated by revolution about y axis do i have to solve the given equation for x?

Find the volume of the solid generated by revolving about the y-axis the region bounded by the curves y = (3x+22)/ sqrt(x^3+11x^2+4), the x-axis, and the lines x = 0 and x = 1.

How would i set this problem up? solving for x in this case sounds impractical
Nicholas Bungershaw - Thu, 01 May 2014 00:29:30 EST ID:7IVXNODr No.13951 Ignore Report Quick Reply
It will be an integral f(x)=(3x+22)/ sqrt(x^3+11x^2+4) bounded from 0 to 1. Wolfram-alpha gives some good visual if your not sure what it's going to look like.
Nicholas Bungershaw - Thu, 01 May 2014 00:33:23 EST ID:7IVXNODr No.13952 Ignore Report Quick Reply
oh, just fyi x values will be the bounds. In problem when they're not given you'll have to solve for them.
Alice Fanningpad - Thu, 01 May 2014 00:36:06 EST ID:dtJRvm7a No.13953 Ignore Report Quick Reply
>solving for x in this case sounds impractical
It is. Do this:

So for your case, you should take the integral from 0 to 1 of 2(pi)*x*y(x)*dx.
Alice Fanningpad - Thu, 01 May 2014 00:47:47 EST ID:dtJRvm7a No.13954 Ignore Report Quick Reply
Comes out to 8(pi).
Barnaby Casslewet - Thu, 08 May 2014 17:21:16 EST ID:m+wesBpj No.13961 Ignore Report Quick Reply
Just use the shell method, make sure your 'slices' with width delta Y are parallel to the Y axis. Seems counter-intuitive at first but it works.

study by blop - Fri, 02 May 2014 15:32:38 EST ID:D6XeU0jB No.13955 Ignore Report Reply Quick Reply
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hey /math/ i am starting to go to school for my GED and would like to find a better way i can work on my math skills at home can some one give me a good site to study pre algebra?
William Fommerhood - Fri, 02 May 2014 17:27:16 EST ID:dtJRvm7a No.13956 Ignore Report Quick Reply

Complex Analysius by Priscilla Masslebury - Sun, 27 Apr 2014 08:52:54 EST ID:GKq/pGEr No.13945 Ignore Report Reply Quick Reply
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Hey math/

What is the significance of Im[ f(u(theta)) ] = 0 ?

What can we say about f(z)? u(theta) forms a continuous closed loop in the complex plane.

In return, tits.
Matilda Bosslestock - Mon, 28 Apr 2014 14:56:09 EST ID:MTIV7/tU No.13948 Ignore Report Quick Reply
Seems to me like the image of the loop is in the real axis.

Class options for next semester by Faggy Bashspear - Tue, 15 Apr 2014 11:21:02 EST ID:D8I2lPwU No.13901 Ignore Report Reply Quick Reply
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I'm a sophomore math major, and next semester I plan to take abstract algebra and either probability or dynamical systems. I'm thinking probability is probably (heh) more practical, but dynamical systems looks like a lot of fun. Do you guys have any input? Should I just take what appeals the most to me?
8 posts and 3 images omitted. Click Reply to view.
Edward Savingwater - Sat, 26 Apr 2014 01:04:07 EST ID:5fuPW64F No.13938 Ignore Report Quick Reply
>-1/12 is the sum of the natural numbers
You are the first person to mention this in this thread.

>type up a reply on 420chan that is longer than the necessary google search
I agree.
Nell Sushfield - Sat, 26 Apr 2014 04:17:11 EST ID:Dk8yywxc No.13939 Ignore Report Quick Reply

>didn't read the thread
Jenny Billerchine - Sat, 26 Apr 2014 11:39:45 EST ID:dtJRvm7a No.13941 Ignore Report Quick Reply
I bet you also believe imaginary numbers are legit and .999... = 1. ;)

You're getting way too rustled over the most common /sci/ troll thread topic.
Nell Sushfield - Sat, 26 Apr 2014 13:08:49 EST ID:Dk8yywxc No.13943 Ignore Report Quick Reply

0.999... does equal one if you are in a system that doesn't allow Infinitesimals, for instance the regular real numbers. If you are in something like the hyperreals, than 0.999... != 1. And yes, I have no problem with imaginary numbers, they're clearly worthy of study.

Stuff like the Ramanujan summation and interpreting these series through the Riemann zeta function is not a "legit" summation, it is a property of the partial sums. We don't know whether the sum 1-1+1-1+1-1... will stop at an odd or even position, so they gave it a value 1/2. That is not completing the summation, it's a property of the partial sums.

The reason I decided to address it is because I've seen it all over the place, not just this site. People like the asshole in that first video will perpetuate this with the goal of "oh science is so cool this stuff adds up to -1/12" while what is really happening is that he's presenting people that aren't familiar with the situation a skewed image that is completely false for the assumption of the average youtube viewer that he is "really" summing to infinity and getting -1/12. I'm not saying that this stuff isn't worth study, but when you have some person with a shit face grin adding up a divergent series to get a negative number, it's doing more damage than anything. Complete misinformation.
Edward Savingwater - Sat, 26 Apr 2014 15:44:19 EST ID:5fuPW64F No.13944 Ignore Report Quick Reply
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wha happen by Jenny Poshmirk - Thu, 17 Apr 2014 12:47:31 EST ID:Hu5XsTVT No.13919 Ignore Report Reply Quick Reply
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What happened to That place was the best to get all of the math books I needed. Are they moving to a new domain, or are they gone forever?
Beatrice Sallerteg - Sun, 20 Apr 2014 00:08:17 EST ID:2aEkBtv5 No.13929 Ignore Report Quick Reply
Hannah Dribbergold - Sun, 20 Apr 2014 17:25:44 EST ID:mgZf5LL6 No.13930 Ignore Report Quick Reply


Gödel's Ontological Proof of a Godlike Being by Shit Buggleman - Sat, 22 Mar 2014 08:00:51 EST ID:gxFYvDAi No.13788 Ignore Report Reply Quick Reply
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More a logic thing - sorry if this is inappropriate. But it delves into a little bit of number theory - all of this is about the picture related.

Gödel's Ontological Proof


Other ontological arguments such as Anselm's or Platinga's are widely held to be deeply flawed.

Anselm defined God as "...that than which nothing greater can be conceived," and then argued that this being could exist in the mind. He suggested that, if the greatest possible being exists in the mind, it must also exist in reality. If it only exists in the mind, a greater being is possible—one which exists in the mind and in reality.

Gaunilo responded to this by pointing out that using the same logical form, you can prove anything. For example, imagine a superlatively excellent island; it would be more excellent to imagine a island with those characteristics that also exists.

That's the typical response. Use the relativity of things to create an infinite chain; which is an absurdity.
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Hamilton Cepperkidging - Fri, 11 Apr 2014 23:15:54 EST ID:pdfJePhZ No.13891 Ignore Report Quick Reply
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i don't understand most of the rest either but i thought i'd understood def. 1, at least in lay man terms since i know the verbal description from wikipedia
>Def. 1:
>god (G) is a function in relation to any element (x) of the set of existing things,
>it is the same (<=>) as the following statement:
>any (aleph) property (phi), if the property is positive (P()), implies the property of an existing thing
> G(x) <=> All phi (P(phi) -> phi(x))
there is much more i didn't grasp, though

i see no clear distinction of a property, a if it's not conventional, "god" is possibly just the sum of all things that have positive traits, isn't it? i find it interesting, just not enough to spend an evening or more reading through wikipedia.
Emma Shittingwill - Fri, 11 Apr 2014 23:54:20 EST ID:gxFYvDAi No.13892 Ignore Report Quick Reply
I feel like the Summa Bonarum is just a lazy way of having your cake and eat it too. Not really worth the term "God" which usually entails more properties. You can define anything as true, or even call any set anything (and in a way defining anything to be the set) but that doesn't mean you get to sneak in the rest of your positions, like pretending the Summa Bonarum includes the Causa Prima, Omnibenevolence, Omnipotence, Omniscience, Omnipresence, Personalness, worship-worthy, mind-independent etc.

But I digress and I guess that's not suited here.
Ernest Trotville - Sat, 19 Apr 2014 08:13:13 EST ID:ndglKlTo No.13926 Ignore Report Quick Reply

So for Axiom #5: Either a property is positive or its negation is, but not both (there are no neutral properties).

Physical matter has neutral and undefined properties as well. Even if the proof is internally sound, does it actually have external validity? If we negate axiom 5, is the proof still valid?
Molly Geppernune - Sat, 19 Apr 2014 16:57:35 EST ID:Ic0nsJzW No.13928 Ignore Report Quick Reply
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I would say it relies on math being the approximation of a priori principles and not rules separate from perception, like Scopenhauer.
To disprove it by counter-example, though it's a bit silly and relies on the abstract, would be
>god is eaten by christians in the form of bread and wine
>this mixture is said to be the flesh of god
>said mixture also has mass (get it?) inside stomache
>said mass is less than stomache's dimensions
>the whole god is described in the process of digestion
Bam, you've defined the indefineable.
James Fumblenotch - Mon, 19 May 2014 01:13:19 EST ID:DMle3oF7 No.13998 Ignore Report Quick Reply
>Physical matter has neutral and undefined properties as well
as far as we, the onlookers are concerned.
>If we negate axiom 5, is the proof still valid?
then the axiom would be meaningless and probably not included.

Series by Emma Gassleville - Mon, 24 Mar 2014 23:56:46 EST ID:GKq/pGEr No.13810 Ignore Report Reply Quick Reply
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Hi /math/, I've got to find the limit as n goes to infinity of the series:

(2/n) . [sum from j=1 to j=n-1 of sin( j.pi / n ) ]

I know the answer is something like 1.2726 by plugging it into a calculator, but I'm lost as to how to prove it.

When I expand it out:

(2/n) . [ sin(pi/n) + sin(2pi/n) + sin(3pi/n) + ... + sin([n-1]pi/n ]

Then expand out the signs using the Taylor expansion I seem to get zero. Any ideas?
2 posts omitted. Click Reply to view.
Barnaby Worthingway - Thu, 27 Mar 2014 04:05:46 EST ID:dtJRvm7a No.13816 Ignore Report Quick Reply
>That's a Fourier series
No it isn't. Fourier series are not functions of the upper bound of the summation as is the case here.

OP, are you satisfied with the answer here >>13811? I could elaborate if you want. What do you need this for - as in - how rigorous of a proof do you need? Some feedback might help.
Fanny Tillingdale - Fri, 28 Mar 2014 22:20:46 EST ID:XeKgjFhn No.13820 Ignore Report Quick Reply
> Fourier series are not functions of the upper bound of the summation
What stops you from evaluating S_n(x) for x=1/n?
Fanny Brookford - Mon, 31 Mar 2014 02:53:08 EST ID:dtJRvm7a No.13832 Ignore Report Quick Reply
S_n(x) is actually S(n, x), and the Fourier series is the limit as n goes to infinity. In a Fourier series, n and x are independent. It doesn't make sense to constrain x as a function of n - it just isn't a Fourier series. The series in the OP can be evaluated without using Fourier series.
Betsy Lightstone - Fri, 11 Apr 2014 22:07:27 EST ID:rMOrE87Y No.13890 Ignore Report Quick Reply
I believe that you can always find if a series is convergent by using the integral test (as long as you can get the integral of your function or reason another sum that would be larger is also convergent). I can't remember if it will be able to give you a value of the sum at infinity or just a bound on the sum though.
Martha Piffingwell - Fri, 18 Apr 2014 21:33:50 EST ID:o/FLjhC/ No.13925 Ignore Report Quick Reply
You can use deMoivre's formula to write (cisx)^n as a sum using the binomial expansion.

Engineering in college by Shit Dremmerwidge - Fri, 18 Apr 2014 03:03:26 EST ID:n9zPhy+9 No.13920 Ignore Report Reply Quick Reply
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Hello /math/,
So I just sent my SIR to UC Irvine. I'm going to be an anteater in the fall! I got $40,000 per year in aid and grants so I'll have minimal debt . I got accepted under polisci because my freshman grades kind of screwed me over. But I got an email yesterday and they told me I could appeal my decision to the school of engineering, which I did. I just had to inform them of my last semester grades and any science-related experiment/project I've done. Last semester I took AVID senior seminar, AP Microeconomics, AP Calc A/B, AP Physics, and AP English lit and Comp. Grades were A, B, A, B, A respectively .
The email also said that they have space in Material Science Engineering and maybe in Aerospace engineering (my preferred choice), but I didn't want to risk not getting in so I chose MSE.
Was this a good choice? Any of you doing MSE? What's it like?
Angus Snodwill - Fri, 18 Apr 2014 10:38:39 EST ID:dtJRvm7a No.13922 Ignore Report Quick Reply

How do I study Micro Economics by Donald Trump - Thu, 10 Apr 2014 19:59:07 EST ID:KRWTY1dS No.13888 Ignore Report Reply Quick Reply
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TL;DR Good ways to study for microeconomics outside of taking notes, reading the book and flash cards
I figured I would put this here since there none of the other boards seem to fit

I am having trouble studying Micro economics
I think I finally took adequate notes but I am not sure what would help me to put them in my brain

normally I make flash cards, retype my notes, practice any concepts I need to know, and on occasion re read the book.
But economy is so in depth on such extremley basic concepts that its hard for me to focus while studying
so my question is, Have any of you taken economy? If so whats the best way to study for it. (My teacher is also a hard ass so tests arent easy)
pic related, Time value of money
Betsy Lightstone - Fri, 11 Apr 2014 21:50:19 EST ID:rMOrE87Y No.13889 Ignore Report Quick Reply
I think you might be equating effort with learning which isn't always true.
Fucking Blythewill - Sat, 12 Apr 2014 21:20:37 EST ID:Rc8L8GaW No.13893 Ignore Report Quick Reply
microeconomics is piss easy
Shitting Murdville - Sun, 13 Apr 2014 04:06:51 EST ID:suSRpPRf No.13897 Ignore Report Quick Reply
Alice Sittingchodge - Mon, 14 Apr 2014 17:42:18 EST ID:ksZJjhPb No.13898 Ignore Report Quick Reply
Go ahead and make flashcards for the vocab
Practice drawing supply/demand curves, and how they move around.
Donald Trump - Wed, 16 Apr 2014 12:17:42 EST ID:KRWTY1dS No.13915 Ignore Report Quick Reply
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I have a lot of trouble studying by just reading, usually my studying consists of writing and rewriting my notes, flash cards, compressing my notes and very little time just reading my notes. is a good way to force things through my brain that otherwise wouldn't go so easily. I have B's in all my classes right now except for econ.
I am not sure whats so hard about his tests. My friend has a different professor and her tests are WAY easier than mine
Practice drawing the graphs is something I havent tried, thank you

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