Math Is Fun Forum

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

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#1 Re: Help Me ! » I hope someones sticky's this "Amazing math resource" » 2010-07-31 10:29:52

AVG? *hurls* I used it for a while before leaving it for avast.

#2 Coder's Corner » ObjC/Cocoa Touch EXC_BAD_ACCESS » 2010-07-16 12:32:17

Replies: 0

If anyone here knows Objective-C...
I am having a problem with an app I am creating. What it does is it opens the app, then immediately crashes. (If anyone's wondering, it's a Tab-Bar based application) The exception I get is "EXC_BAD_ACCESS". So as any good programmer does in a situation like this, I googled the error. It turns out that that happens if a command is passed to a released object, this exception is thrown. I also learned about NSZombieEnabled. That is supposed to print out the command that is causing the exception. But when I go into the console, nothing is printed out! I think it has to do either with the default files that come with the Tab-Bar application, or with the .xib files I have. I think this because I copied over the .xib files to a new (Tab-Bar based) application, and the same error occurred. I'm just about to throw in the towel on this one, so if anyone knows what to do here, please let me know.

#3 Re: Dark Discussions at Cafe Infinity » Make proposals to stopping the oil leakage in the mexican gulf » 2010-06-22 04:01:25

Well, obviously, if the point is somewhere near a city, we shouldn't try that approach.

#4 Re: Dark Discussions at Cafe Infinity » Planet Killer? » 2010-06-21 10:16:12

Actually, I read in the news a while ago that there is a kind of bacterium that puts out a substance that can be used for fuel. Maybe that's the source of the replenishing oil. (Although it could have not been oil. I just can't remember.)

#5 Re: Dark Discussions at Cafe Infinity » Make proposals to stopping the oil leakage in the mexican gulf » 2010-06-21 10:05:09

Depending on the currents in the Gulf, there may be a single point where the oil may converge. If that is the case, then once the oil settles, you could remove it much more easily.

#6 Re: This is Cool » Prime Numbers!! » 2010-06-21 09:53:39

Primes in Computer Encryption
Huge primes are used in computer encryption, which was explained very well in a post by mathsyperson: (I'm paraphrasing, as the post was long, and I can't find it.)

mathsyperson wrote:

Let's say that Person A wants to send something through the mail to Person B. It is of considerable value, so A wants to make sure that it is not stolen. However, shady Person C (who happens to be the only mailman for miles around) wants to steal it. So Person A puts a lock on it. However, Person B doesn't have the key to the lock, so B puts another lock on it and sends it back to A. A takes his lock off, and sends it back to B. B takes off his lock, and the item is safe, even though both have probably spent their life's savings on locks, and shipping costs. With hackers, it's the same deal, except valuable items are replaced with valuable data, and locks are replaced with very, very large prime numbers.

Mersenne Primes and the Prime95 (GIMPS) Project
Mersenne primes are prime numbers of the form

. 3 is a Mersenne prime - it is equal to
. GIMPS is an acronym for "Great Internet Mersenne Prime Search". It is a large program built up by many computers that are searching for Mersenne Primes with unused memory.

#7 Re: Help Me ! » entering a function into graphing calculator » 2010-06-21 09:34:42

Bob bundy makes a good point. Another thing that I can do on my TI-84 Plus Silver Edition (Maybe it works on the TI-83, I don't know...) is to input y=±√x.
Another thing you could do is use the "Implicit Grapher" here on Maths Is Fun. You could input x=y² on it.

#8 Re: Maths Is Fun - Suggestions and Comments » Matrix Calculator » 2010-05-19 13:48:56

The only complaint I can think of probably doesn't apply to many people here, but if both matrices are 10x10, then B gets cut off.

#9 Re: Maths Is Fun - Suggestions and Comments » Logging in twice » 2010-04-27 12:16:19

Thanks for the help guys!
I haven't gotten it to happen recently, so I must have done something that made it stop... so that means that it is a local problem.

#10 Re: Maths Is Fun - Suggestions and Comments » Opinions on Style Please » 2010-03-13 11:59:42

To me 2 and 3 look the same, and I like them both.

#11 Re: Help Me ! » I need a descriptive geometry book » 2010-02-07 06:43:17

Don't know about the pdf downloadable part, but here's a really good book: Introduction to Geometry by Art Of Problem Solving. They have a few other good things on their website, including FTW. Their website is:

#12 Maths Is Fun - Suggestions and Comments » Logging in twice » 2010-02-07 06:33:49

Replies: 4

For some reason, I sometimes need to log in twice to actually get logged in. When I log in the first time, it goes back to the normal page when you are not logged in, with the log-in fields at the left. It does do the "Logged in successfully" screen. It does it in both Firefox and Chrome. I haven't tried it in any other browsers.

#13 Re: Help Me ! » How do you join the Forum? » 2009-12-30 10:14:09

It is legal for you to sign up for gmail ( if you are 13. If your parents won't let you, they may let you use their email.

#14 Re: Coder's Corner » Python Variable Definition Troubles » 2009-12-26 06:50:48

True, but that doesn't explain why it works on Windows, but not Mac.

#15 Re: Coder's Corner » Python Variable Definition Troubles » 2009-12-24 07:44:26

Sorry to double post, but I noticed that a Windows machine with the same installation of Python doesn't have a single problem.

#16 Coder's Corner » Python Variable Definition Troubles » 2009-12-23 14:32:30

Replies: 5

I'm trying to make a Mafiya game in Python, but have run into problems. Here's what I'm worried about:

import random

def Start():
    day = 0 #This variable definition should work...

Here's what I get when I run it:

Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
  File "/Users/Rayment/Documents/Chase/games/Python/Mafiya!", line 5, in Start
  File "/Users/Rayment/Documents/Chase/games/Python/Mafiya!", line 7, in DayTime
    day = day + 1;
UnboundLocalError: local variable 'day' referenced before assignment

I know that means that my variable definition is wrong, but it should be right. What gives?

#17 Jokes » Wolfram|Alpha Jokes » 2009-10-08 12:24:58

Replies: 1

Wolfram|Alpha tells jokes when you search "tell me a joke". (They are all mathematics-related.)

#18 Re: Jokes » Never tell a lie » 2009-10-06 13:33:02

Oh, not all reverends say one thing and do another.

#19 Re: This is Cool » Another..nother number trap. » 2009-10-05 12:43:03

True, so let me restate that:
I wonder if this can be proven mathematically for the English language.

#20 Re: Jokes » Never tell a lie » 2009-10-05 11:23:31

Nothing against reverends, though. Not all of them are hypocrites.

#21 Re: This is Cool » Another..nother number trap. » 2009-10-05 11:20:56

I wonder if this can be proved mathematically.

#22 Re: Help Me ! » Combination Problem » 2009-10-05 11:18:40

Here's another way:
Think of the formula for


Now rewrite
using that. You should be able to solve for n.
Tell me if you need any more help.

#23 Re: Maths Is Fun - Suggestions and Comments » Implicit Equation Grapher » 2009-10-05 11:14:07

One thing I'd like to see is recognizing that xy is the same thing as x*y.
Another one I like is tan(x*y)=sin(x)+cos(y).

#24 Re: Help Me ! » grapf » 2009-10-04 09:11:09

Hmm... that's not making much sense to me. Do you mean:

If you do, you can start by plotting points. Then plot those points on graph paper. Find a point equal distances away from each of the points. That'll be your center. Then find the before mentioned distance. That'll be your radius.
If I interpreted that wrong, please let me know.
EDIT: If you need to do the second part algebraically, the number after the = is always the radius squared. Take the square root of that.

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