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#526 Re: Help Me ! » Integration » 2007-06-05 17:44:31

Draw the function, sketch the volume after rotation.
Slice the volume vertical to x axis and then integrate.

#527 Re: Dark Discussions at Cafe Infinity » Innovation ain't always good » 2007-06-04 21:35:11

Well, at least they say the colour may change; the background may be omitted in certain occassions.
Acctually I am not quite appreciating the first one-nice but a little bit sparse, just that the second is too horrible.

For Beijing Olympics, you cannot miss the artistic torch, and the special medals! The torch has many clouds figures on it, revealing a beauty of complex. The gold madals are made of gold and a kind of precious stone, Hotan Jade. The Hotan Jade is as hard to carve glass but it wears a smooth and friendly look. Other madals use different jades. Interestingly, though, jades represent the cultural idea similiar to gentlemanship-polite and friendly, but can be very determined when meeting confrontation. (It touches smooth, looks nice, but it will rather collapse than bend under force) And Hotan is best of its kind, because it's the nicest on the surface while hardest inside. However the medals have only passed 3 metre free fall test, so be careful winners!

To be frank, the Olympic arena doesn't look nice. It looks a little bit chaotic and too artificial-I mean an environmentalist may dislike it. Anyway, I didn't vote for it but it won out from several designs. The water stadium (for swimming kind of sports) is interesting-a huge bubble box, yet I just wish the bubbles were brighter.

#529 Dark Discussions at Cafe Infinity » Innovation ain't always good » 2007-06-04 15:26:15

George,Y
Replies: 6

2DCAAC29F35DDF1F6C5A3A8DB09DBE4F.jpg
1A1D2ED620A1F7076A0CE7E145428B00.jpg

Which looks better?






The former is the logo of 2008 Beijing Olympics, while the latter is the one of 2012 London Olympics.

You may note a distinct contrast of the latter to the former as me
-black background vs white background, angle numbers vs round numbers, words inside numbers vs outside them.
This is truely an attempt for speciality, but does it work?

Change can get a better result, however it can also get a worse one.

#530 Re: Dark Discussions at Cafe Infinity » Basic Quantum Physics » 2007-06-04 15:19:06

I don't understand the one photon at one time experiment. Really weird. The Photon splits into two parts of itself before it sees two slits?? Really weird.

But can anyone explain why it won't work when two slits are wide or distant from each other?

#531 Re: Help Me ! » factoring i and complex expressions » 2007-06-04 14:15:51

The solution for two complex numbers to multiply to a given one is Not Only. They are a lot. Think of one pair, then I multiply one of it by a complex factor, and divide the other by the same factor, woo! another solution pair!!

So after some analysis, the only way to get your convenient solution (ideally integer coefficients) is to guess.

#532 Re: Help Me ! » Comparing interest rates » 2007-06-04 14:07:36

No, after one year or two, Ben's is still better than Simon's-that's why I said it depends.
Ben's curve is a linear one with a good beginning, while Simon's is an exponential one with a poor beginning. In the long run, first interest of the latter will meet the former or even overnumber the former and then keep increasing the gap, after a while the total sum of money of the latter will drawf the latter.

However, "the total sum" does not count in reality. Today's one dollar is different than that after a year. Because bank and interest rate exist.
100today=100(1+interest rate) next year
100/(1+interest rate)=100 next year.
Under this consideration, we can transfer the cash gains of respective years all to equivalent gains today and sum them up, to so called Present Value. And if the compound rate 6.5% is less than the bank interest rate, there is no guarantee for it to beat the annual earnings.

#533 Re: Help Me ! » Comparing interest rates » 2007-06-04 03:08:12

But, how can you draw a graph of 1.065^x without knowing the values?
I guess you have gotten a table already, to help you calculate interest rate.

It simply depends, Jane.
Given the total time, a high simple interest rate can beat up a low compound interest-rate.
And typically monthly savings is less profitable than annual savings, because you pay more for the latter-you pay the promise of not withdrawing it for a Whole year.

#534 Re: This is Cool » easy proof of the chain rule? » 2007-06-04 03:01:11

Well the infinite series thing is applied by taking a finite part of it. So Maclaurin series is very useful in getting any digit we want.

#536 Re: Help Me ! » Comparing interest rates » 2007-06-04 01:24:22

Basically yes, but 12 should be replaced by 4 because of the word "quaterly".

#537 Re: This is Cool » easy proof of the chain rule? » 2007-06-04 01:18:55

you can search "The radius of convergence" for more details.

#538 Re: Dark Discussions at Cafe Infinity » Harry Potter, Voldermort and the other that survives. » 2007-06-03 20:58:20

I think maybe at last Harry and Vordermolt just cancel out each other, as Neo and Mr.Smith did in Matrix.

#539 Re: This is Cool » easy proof of the chain rule? » 2007-06-03 13:56:28

Not so, some cannot. Divergency problem.

#540 Re: This is Cool » 0.9999....(recurring) = 1? » 2007-06-03 03:09:19

Very passionate indeed.
Zach, would you mind checking up post 735 too? A little far, though.

#541 Re: This is Cool » easy proof of the chain rule? » 2007-06-03 02:54:59

The biggest flaw of your proof is assuming Δg≠0 always, as long as x around the intevals of x[sub]0[/sub]

Here is a proof covering all points when Δg=0. Elegant.

The Proof

#542 Re: This is Cool » The Classic Slide Rule » 2007-06-02 20:55:57

This post is on what can we find only by looking at the LL scale

Here is a photo of a slide rule
click while pressing "shift" to get the pic in a new window

So you can observe the first side of the slide rule.
Note the bottom and the upper part. LL3 LL2 LL1 LL01 LL02 LL03
A little bit confusing.
But just drag the slide bar at the bottom of the window and check the right end of the slide rule.
The mark


And notice the x mark to the right of D scale.
Yes, exactly LL scales are exponent scales of D, note that D is already exponential. So e^D=e^(10^L). Note that LL3 scale increase dramatically.

Other than telling exponent of e and ln backwards,
having these 6 scales of exponent brings about two benefits.

One is that you can easily get the power of 10th or 1/10th easily.
Because e[sup]x[/sup]=e[sup]0.1x×10[/sup]= (e[sup]0.1x[/sup])[sup]10[/sup]
Check 2 on LL2 and the value on the scale above, the LL3 scale. 2^10≈1.03×10[sup]3[/sup]
Yes, if you are familiar with computer, 1KB=2^10Bytes=1024Bytes. 1030 is close to 1024, as far as the slide rule can tell.

Another benefit is the inversions
Because e^x=1/e^(-x) and so on, you can check inversions by two corresponding LL scales. LL3-LL03 LL2-LL02 LL1-LL01. The small scales of LL1 and LL01 can give very accurate inversions of numbers near 1. Suppose you are calculating how much you need to save under the interest rate at 3.5 to get 1000 next year. 1/1.035 is needed. By checking I can see it's 0.9656.

Additionally, just check the positions of 1.01 1.012 1.02 1.03 1.04 on LL1 and 1 1.2 2 3 4 on D. You will notice their positions are near, horizontally.
This is because e^x ≈ 1+x when x is small.
So e^.01x ≈1+.01x
The formula can be derived by derivative:
(e^x)'=e^x
e^(0+h) ≈e^0+(e^x)|'[sub]0[/sub]h- h is small.

#543 Re: This is Cool » The Classic Slide Rule » 2007-06-02 20:06:42

Next, LL scale.

Observing LL scale
Using LL scale

#544 Re: Help Me ! » Calculus: some problem with limits... » 2007-06-02 20:03:32

I see, the power law is something like a shortcut.

#545 Re: Help Me ! » Are remainders always positive or can they be negative. » 2007-06-02 14:14:33

Yes, for convenience we use a remainder satisfying 0<remainder<divident.

#546 Re: Help Me ! » Calculus: some problem with limits... » 2007-06-02 14:08:06

Standard proof:

When f(x)->a and g(x)->b and b≠0
lim[f(x)/g(x)]=a/b

#547 Re: This is Cool » 0.9999....(recurring) = 1? » 2007-06-02 13:47:39

What Ricky has argued is not a good point.

Because he simply double-use the concept.

If Ricky is Ricky with an apple.
Definately Ricky without apple is not Ricky with an apple.
Yes we can say both Ricky with or without apple are  Ricky, but two Rickys have difference for sure, which cannot be ignored only by using the same name "Ricky".
A box empty and a box with at least an apple are two different things. You can say they look just alike, but that doesn't mean they are strictly equal.
1-infinitesimal if=1
then infinitesimal=0
then 0.999... can only have finite digits because the digit at the end and the those before it =0 too.
if the infinitesimal ≠0
then 1-infintesimal≠1 (without the apple)
However if you say infinitesimal=0 and infinitesimal≠0 can exist at the same time, then I have few words. But let's consider the counter-situation: at the occasion you say it=0 I say it≠0; in the time you say it≠0 I say it=0 -which seems can exist, too.

#548 Re: This is Cool » 0.9999....(recurring) = 1? » 2007-06-02 13:37:33

Anthony.R.Brown wrote:

So there we have it! the True Value for Infinite/Recurring 0.9 IS! Infinite/Recurring 0.1 < 1

We dont have to know how many Decimal places! just that 0.(n) will always be < 1

A.R.B

Yes, let's just ignore the controversial infinite digits and have simple but elegant finite assumption.

#549 Re: This is Cool » 0.9999....(recurring) = 1? » 2007-06-02 01:59:06

spontaneous multiplication rate is human's imagination.
Bacteria can only do discrete multiplication.

#550 Re: This is Cool » 0.9999....(recurring) = 1? » 2007-06-02 01:57:29

e is definitely another approximation of finite things

The bacteria multiplication is
1 2 4 8 16...
not
1 e e^2 e^3...
Asking the problem of having all the digits( an infinite amount) of e has no meaning.
You will never calculate that out either. (you and a computer can only calculate an Finite amount after a finite time)
e^x if fitting the data, ok. 2^x also. If you are convenient with e^x, fine. but keep it in mind actulaly no spontanous growth rate or multiplication thing in reality, only in human's mind for convenience.

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