 mersenneforum.org > Math Proof of LL theorem
 Register FAQ Search Today's Posts Mark Forums Read  2006-02-15, 10:04   #45
Numbers

Jun 2005
Near Beetlegeuse

22·97 Posts I am obviously completely thick, because I still don't get it.

Quote:
 Originally Posted by Alpertron You set arbitrarily the value y=3, that does not give integer values for and .
Well actually no I didn't arbitrarily set y=3. I just used the first Pythagorean triple I thought of; y = 3, x = 4, z = 5 and showed that if (x, y, z) are a Pythagorean triple then does not have to be of the form 2pq. Since you seem to be under the impression that I chose this deliberately, I will now choose y = 4 (the other possible definition of y from this same triple) and show exactly the same thing.

Let , , form the Pythagorean triple .

You say that it follows that from which

we get that which factors as

either or .

So, .

You say .

or gives us , or .

or gives us , or .

I don't see a 9 in there, do you?

Then you say, .

or gives us , or .

I don't see a 25 in there. Do you?

So, using the very first Pythagorean triple I could think of I have shown that it definitely does not follow that if then , completely irrespective of which term you call y.

So there is no logical sense in which you can claim that it follows. Because, it does not.

You might be able to start with and and construct a Pythagorean triple in which it is true. But it does not "follow" from three integers being a triple.

Quote:
 Originally Posted by Alpertron Have you ever seen a proof by contradiction?
Formally, no. But I have seen things like the proof of the infinity of the primes. A proof by contradiction starts by assuming a statement P to be true. Then it shows that this leads to a contradiction and the assumption is that therefore P is not true.

My understanding is, however, that the route to the contradiction has to consist of one or more logically sound steps. I am not yet in a position to agree that your first step is logically sound.   2006-02-15, 10:42 #46 Kees   Dec 2005 110001002 Posts Before we rewrite history by saying that pythagorean triplets do not work... a^2+b^2=c^2, gcd(a,b,c)=k then a = k * (p^2-q^2) b = k * 2*p*q c = k * (p^2+q^2) in the simple case 3^2+4^2=5^2 we get 3 = p^2-q^2 4 = 2pq so p=2 and q=1 which leaves p^2+q^2 = 2^2+1^2 = 5 = c This is not a demonstration, but just shows that the pythagorean triplets are not completely off   2006-02-15, 10:56 #47 Numbers   Jun 2005 Near Beetlegeuse 38810 Posts Aha!. so what your saying is that it isn't It is in fact . Thank you kees for that clarification. No doubt someone will now accuse me of being pedantic.   2006-02-19, 13:14 #48 alpertron   Aug 2002 Buenos Aires, Argentina 135610 Posts But 3^2 and 4^2 are not fourth powers!!! If x^4+y^4 = z^2 it should be clear that x^2 = a, y^2 = b, so y^2 = 2pq.   2006-02-19, 14:09 #49 Numbers   Jun 2005 Near Beetlegeuse 22·97 Posts Alpertron, Everything you have said is absolutely correct. All that happened was that I failed to make a simple connection between two statements you made in post #22. Lets look at two simple identities: ..................(A) .......(B) When we see them together it is immediately obvious that the in (A) is equivalent to the in (B). I, however, failed to make this connection. So, when you said that I was trying to derive this from (A), but should have been looking at (B). In other words, I am a completely stupid idiot and you are very patient gentleman. Thank you.   2006-02-19, 15:35   #50
mfgoode
Bronze Medalist

Jan 2004
Mumbai,India

22×33×19 Posts Proof of LL theorem

Quote:
 Originally Posted by mfgoode If Numbers is not content then try this URL. http://homepages.cwi.nl/~dik/mathematics/jsh2.html Mally  My entire post on PYthagorean Triplets has been erased but I have it saved and wonder if I should repost it.
Mally    2006-02-19, 15:41   #51
mfgoode
Bronze Medalist

Jan 2004
Mumbai,India

22·33·19 Posts Quote:
 Originally Posted by Numbers Alpertron, In other words, I am a completely stupid idiot and you are very patient gentleman. Thank you. I doubt you are as you are a skilled sophist.
Its not good to give in to Self Pity. 'Beware the ides of March'
Mally    2006-02-19, 16:09   #52
alpertron

Aug 2002
Buenos Aires, Argentina

22·3·113 Posts Quote:
 Originally Posted by mfgoode My entire post on PYthagorean Triplets has been erased but I have it saved and wonder if I should repost it. Mally    2006-02-20, 18:03   #53
R.D. Silverman

Nov 2003

22·5·373 Posts Quote:
 Originally Posted by TravisT I'm halfway through my abstract algebra series (Up through chapter 6 in Artin's Algebra, if you're familiar with it) I know Lagrange's theorem, however, I don't think we've gone over multiplicative sub-groups of a finite field just yet. Would you mind going over the proof with some pointers of where I should do my homework to understand the bits I don't know?

Sure. All you need to know is that for a prime p, GF(p^2) has
a multiplicative subgroup of order (p+1). Look at the elements of
GF(p^2) whose inverse equals their conjugate. Now just find an
element of full order in this group, and show that x_{n+1} = x_{n}^2 - 2
is just doing exponentiation in this group in disguise.   2006-02-21, 14:54   #54
mfgoode
Bronze Medalist

Jan 2004
Mumbai,India

22·33·19 Posts Proof of LL theorem

Quote:
 Originally Posted by mfgoode My entire post on PYthagorean Triplets has been erased but I have it saved and wonder if I should repost it. Mally Resending my post.
As a footnote to this debate I append the following facts on Pythagorean Triplets (Py. Trips.)
1) Pythagorean Method: For all odd numbers (no.s)
If m is an odd natural no. then
[(m^2 + 1)/2]^2 = [(m^2 – 1)/2] ^2 + m^2
Eg: If m = 17, we get 145^2 =144^2 + 17^2

2)Plato’s method: For any natural no.
(m^2 + 1)^2 = (m – 1) ^2 + (2m)^2 where m is a natural no.
Note: Since (m^2 + 1) and (m^2 – 1) differ by 2 in this formula those no.s differing by 1 cannot be given eg: 7, 24 , and 25 as 24 and 25 differ by 1

3)Euclid’s Method : If x and y are integers and if
a = x^2 – y^2; b = 2xy ; c =x^2 + y^2 t hen a, b, c, are integers such that
a^2 + b^2 = c^2.
These formulae should generate all possible Py. Trips.
I hope this clears the doubt and debate.
Mally    Thread Tools Show Printable Version Email this Page Similar Threads Thread Thread Starter Forum Replies Last Post McPogor Miscellaneous Math 18 2007-10-19 11:40 vtai Math 12 2007-06-28 15:34 bdodson Lounge 6 2007-03-19 17:19 mfgoode Puzzles 9 2006-09-27 16:37 jinydu Math 5 2005-05-21 16:52

All times are UTC. The time now is 02:02.

Wed May 12 02:02:00 UTC 2021 up 33 days, 20:42, 0 users, load averages: 2.29, 2.16, 2.30