Math Is Fun Forum

  Discussion about math, puzzles, games and fun.   Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ • π ƒ -¹ ² ³ °

You are not logged in.

#1051 Re: Dark Discussions at Cafe Infinity » Carrots » 2006-10-25 17:41:53

oil stirfried carrot contains abundant vitamine A, which really helps your eyes.

#1053 Re: Help Me ! » Spearman's rank correlation coefficient » 2006-10-25 17:35:53

Sure, actually you can look at a Econometric book, which has many empiracle fromulas.

2 variables just for simplicity and nothing else.

#1054 Re: Help Me ! » Another Physics Problem » 2006-10-25 17:32:00

It's like somebody behind you just push you, and you push someone in front of you, and they are not the same push.

#1056 Re: This is Cool » Mathematical Intuition/Feeling ? » 2006-10-25 03:06:51

Well, I think that may largely lies in transition of knowledge, that when you have a concept, it is similar to a concept you've learned. My instance: determining how many digits of a product in Help section, I unconciously borrow the sandwich theorem in calculus.

In common reasoning, one will think step by step, having little chance to get a leap of reasoning all of a sudden. And if so, I guess it will be sheer guess.

What about your experiences? May you analyze them, and see if my hypothesis stands.

#1057 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-25 02:55:54

Yes, thank you for your surf. I will read it through.

#1058 Re: Help Me ! » Graphing a Circle » 2006-10-24 20:16:40

However, you can try parametric plotting, such as (5cos(t), 5sin(t)), where cos(t) and sin(t) are well defined as functions.

#1059 Re: Help Me ! » Another Physics Problem » 2006-10-24 20:14:38

the difference lies in which object they act on.

#1060 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-24 20:11:51

And what do you mean by infinite series? Can I think of it having infinite entries? So what does "infinite" stand for when you deny infinity as a number?

#1061 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-24 18:45:54

Ricky wrote:

We define the sum of an infinite series to be the limit that the sum approaches.  It is this definition of "sum of an infinite series" which Reimann used and it is Reimann Sums which are used to define integrals.

No infinitesimals even mentioned.

Can you explain Reimann Sum a little bit further? how about the entry of the infinite series? If the series has infinite entries, each entry should be a particular infinitesimal to enture the sum to be a number, I suppose. And this involves a quasi-zero*infinity trick.dizzy

#1062 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-24 17:30:07

"Integrals are done on the assumption that there are no infinitesimals."
-The sum will never reach the amount to which the limit approaches unless the pieces being divided into full-developed infinitesimals.

"0 is not an integer?"
-First, having to be Integers but not all of them. When applying integers, you are not dellusioned to foolishly devide an amount by 0, and you know perfectly the denominater is an integer Except 0. But common economic books give a continueous curve to plot the function, with "AVC" beside vertical lines on the left, which is definately misguiding. If a discrete step by step, no one will make that mistake.

"closing" basis?
yes, N-∈ or Delta-∈ defination by Cauchy, which does not state "reaching" in any conditions.
Besides, do you know where epsilon comes from? One book I've read say it is from the ancient greek word " error".

"We can not infinitely measure anything.  Thus, any statements about the exactness of the universe is pure speculation and nothing but."
-Actually infinity concept is fundamentally flawed proven by simple reasoning and have no reason to exist, which I shall illustrate later.

#1064 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-24 15:37:25

Yeah, I know that- anything relating to limit have something to do with this defination, derivatives-tangents, magnitudes(with nabla notations),and all kinds of integrals.

But the defination only assume their accuracies instead of their more-or-less nature. I bet a electrodynamic professor will advice you to use integrals wisely because there are no infinitesimals in practice. Rather, there are sufficiently small masses of electrons and small scanties of electrons. Thus the theoretical results produced via infinitesimals may be a little bit different from a reality consisting of discrete particles. And in economics you will meet a great trouble if you interpret the Average Fixed Cost- =Fixed Cost/Quantity- as infinity when no product is produced. The solution is to realise the quantity should be integers instead of reals, which have been adopted only for the  convenience to apply calculus.

Hence the exactness might be some pure imagination in mathematicians' mind, and the difference between "exactly the same" and "just a little bit different" can be too small to test. And when it can be tested,  they just deny the reality. For example, they blame the reality cannot give a perfect circle(a polygon with infinity sides).

And I doubt the importance you've stated, for before Georg Cantor the calculus had been on a "closing" basis for so many years and it had been applied so well.

#1065 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-23 17:26:43

I am glad that you finally realised there has to be a defination to fill the gap between finite logic to infinite framework. And that's the point I've been standing at.

Hence any proof of 0.999...=1 is a somewhat equivalent of defining 0.9+0.09+0.009...=1 when by finite logic we know the addition approaches it, and they lose their use. We all know perfectly 0.999... (growing) approaches 1, then why just state honestly we can define it as 1 as it imaginarily come to infinite digits?

Still, I am happy we get a consensus.

#1066 Re: Dark Discussions at Cafe Infinity » France may limit freedom of speech! » 2006-10-21 18:42:29

Recently they wanna move one step further to make personal blogs registered under real names, two years after they did the same thing to campus forums. Guess what they say? Freedom is not absolute. Can they report what they do everyday in government to us, for the freedom is not absolute thing? "Management"- so we are doomed to be censored and controled and "cared" by the big father, huh?

#1067 Re: This is Cool » 0.9999....(recurring) = 1? » 2006-10-21 18:33:38

Because Dross want to prove 0.9+0.09+0.009+...=1
And if he use a limit proof, he is supposed to get 1-0.9-0.09-...=0. Only by this way can Dross get a reaching back-up by limit theory. epsilon means still difference, not 0 though can be any small, doesn't it?

#1068 Puzzles and Games » 6 Frogs Want The Other Side » 2006-10-20 21:53:18

George,Y
Replies: 3

6 Frogs are on a trunk across a small, say, river, 3 facing 3. They wanna get to the other side and none of them would back up to show timidness. A frog can leap forward one step or two steps so long as there is a room for it to land. Now a space for only a frog lies in between of the two groups  and they sit close to each other. Like this
///_\\\
The question, how can they swop the position with the other side and get this?
\\\_///

Apparently after the first step the positions could be
either //_/\\\ or /_//\\\
for convenience, let us use o instead of _ to express the empty space.

It may take you some tries though.

#1069 Re: Euler Avenue » Straightedge and compass constructions » 2006-10-20 15:51:56

If you want to duplicate the length of a line segment, you just need a compass.

If you also want the same direction, construct a parallel line first.

#1070 Re: Dark Discussions at Cafe Infinity » France may limit freedom of speech! » 2006-10-20 15:45:21

It's been limited in my country for a long long time...

#1071 Re: Dark Discussions at Cafe Infinity » Languages; What Are Yours? » 2006-10-20 15:42:26

I can speak
Chinese( Standard Mandarin)
English

Actually I wanna know why is  it named Mandarin? Because the Mans ruling China hundreds of years ago applied it?

#1073 Re: Introductions » Back again » 2006-10-20 15:28:26

Hey, I like maths in practice, too!

#1074 Re: Help Me ! » Differentiation Problem » 2006-10-20 15:21:20

I mean, how many times is 1 as  nothing?

#1075 Re: Help Me ! » Differentiation Problem » 2006-10-20 15:19:15

Yes, you've found it out! Infinity here in fact means some 1/0 or a/0, derived by x and y displacement.

Actually the slope is a kind of directional thinking while the real world is not.

Think of this argument.

Tom loves Maria. So they get married.

In fact it should be this: Tom loves Maria, while Maria loves Tom. So they get married.

The y-x slope is just a tool looking at a line's angle by checking some displacement of x and y from y to x. There is, though, another alternative, x-y slope. And this slope should be 0 without any doubt or undefination.

Board footer

Powered by FluxBB