Proof by Contradiction
The Pythagorean Brotherhood
It is possible that it was a group who called themselves The Pythagoreans, after their founder Pythagoras, who came up with the idea of proving something by contradiction.
The Pythagoreans had a large following and the Pythagorean brotherhood were sworn to secrecy. Its members were dedicated to the pursuit of truth and using mathematical proof.
The truths they discovered then hold true to this day.They succeeded in revealing the objective and timeless nature of Mathematics but because they took and oath of secrecy most of their discoveries died with them.
reductio ad absurdum
The Latin name for “Proof by Contradiction” is reductio ad absurdum and it has proved to be one of the more useful principles of Mathematics to date.
Proof by Contradiction is based on the principle that if you want to prove something is true you first suppose that it is false and then proceed until you find something in your argument to contradict your supposition that it is false.
Irrational
This article is dedicated to one particular problem which dates back to the Pythagoreans and how the problem was solved using Proof by Contradiction.
The Problem:
Is there a fraction which when squared will give an answer of exactly two? Stated mathematically, do the whole numbers x and y exist where y is never zero such that (x/y)^{2 }= 2
QED
We could keep going forever getting and unending sequence of equations always finding a positive number to satisfy each one then this contradicts the notion that any decreasing sequence of positive whole numbers must come to an end.
The fact that we are getting an unending sequence of equations we have proved by contradiction that we cannot find two whole numbers x and y with ration x/y that when squared will give 2 precisely.
Assumptions
There were three assumptions used in this proof because their validity had been proved in earlier.
The assumptions were;

The square of an odd number is always odd

If an integer is not odd then it must be even

Every decreasing sequence of positive integers must end.
Video
Following is a slightly different proof but it still uses the principle of Proof by Contradiction.
Proof by Contradiction in Action
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Comments
I used to teach that.. good on you.
I enjoyed your Hub. It brought back memories of of my college days. I remember finding it fun trying to solve algorithms. I once had a final exam where the proof had no final outcome. I think it was proof by contradiction. Your Hub made me remember that and understand it better than I was taught back then.
A number of times in my life since college I would use algebra to figure something out. It's a useful tool for a different way of thinking. You might almost think of algebra as a language. Every language offers a unique way of thinking or carrying on a thought process. That's something I've recently been studying.
Your Hub was very enlightening. Voted up.
Yours is much more thorough than mine! I should have checked first. Nice job :)
Excellent Hub. I am a historian, not a mathematician, and Algebra was never my forte, although Geometry was, but I teach a History of Science course and we briefly discuss the secretive Pythagoreans. What great intellectual fun and right before Christmas! Thank you. :)
Great observation Mr. Spirit Whisperer (about the emotion part). Thank you!
This is a little off topic but do you think the study of math stuns creativity? (I think it somewhat does ...)
Sorry I cannot comment on the problem/equation: for me, numbers no longer have much of the meaning that mathematics imposes on them.
Cheers!
I enjoyed your Hub on "reductio ad absurdum." It is well done and thoughtprovoking. Thank you!
Math is not my forte, but the premise, here, is fascinating. (I keep kicking myself for not wanting to understand algebra better in my younger years. I did not realize until later that it taught us different ways of thinking and understanding the relationships between variables. ) Thank you for this very interesting read.
Hi Spirit. If the teachers had made Algebra this fun & interesting might have done better in it. Thanks for the bit of history on the Pythagorean Brotherhood too.
I was not able to understand why both the numbers must be positive. Squaring a negative number also yields a positive integer right?
Is it maybe because, for the next step, you will not be get the root for a negative fraction?
If that gets clarified, it will be wonderful......Very interesting thought.....
Thanks for the hub
Hi You lost me with the math; I just can't concentrate these days. But the method of proving things by contradiction makes sense. Probably why no one could ever prove that a god exists...Bob
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