A problem involving the addition of two cubes

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Discussion Overview

The discussion revolves around the exploration of integer solutions to the equation involving the addition of cubes, specifically the equation \(a^3 + b^3 = c^3\). Participants engage with historical references and the implications of Fermat's Last Theorem, while also considering related equations and examples.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant presents a hypothetical scenario where an algebra teacher seeks integer examples for \(a^3 + b^3 = c^3\).
  • Another participant references Euler's work from 1753, although the specifics of his methods are unclear.
  • There is a mention of Fermat's Last Theorem, suggesting that no positive integer solutions exist for \(a^3 + b^3 = c^3\).
  • Some participants propose that there are integers \(a, b, c, d\) such that \(a^3 + b^3 + c^3 = d^3\), providing an example with specific integers.
  • One participant claims there are infinitely many solutions for \(a^3 + b^3 = c^3\), though this assertion is met with confusion.
  • Another participant points out that certain integer triples, such as \((a, 0, a)\) and \((a, -a, 0)\), are solutions to the original equation.
  • There is a suggestion to explore whether similar parameterizations for \(a^3 + b^3 + c^3 = d^3\) can be established as done for \(a^2 + b^2 = c^2\).
  • A participant acknowledges the trick nature of the original question, indicating a playful tone in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on the existence of integer solutions for \(a^3 + b^3 = c^3\), with some asserting that no positive integer solutions exist, while others propose specific cases and alternative interpretations. The discussion does not reach a consensus on the validity of these claims.

Contextual Notes

The discussion includes references to historical mathematical theorems and concepts, but the assumptions underlying the claims about integer solutions are not fully explored or resolved.

Charles Link
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TL;DR
Hypothetical situation: An algebra teacher was looking for examples of how the cubes of two integers might add to be the cube of a 3rd integer. Can you help the algebra teacher?
This post is meant to be a fun one. It is at the beginner level, because I think most people at the intermediate level would know what the solution is, but they might also find it entertaining as well. ## \\ ## A hypothetical situation: An algebra teacher observed that ## 3^2+4^2=5^2 ## and ## 5^2+12^2=13^2 ## and quite a number of others. The teacher wanted to give the class a little practice with some 3rd power arithmetic, and was looking for some integer examples where ##a^3+b^3=c^3 ##. Can you help the algebra teacher find a couple?
 
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Euler, 1753, but I don't know how he did it.
 
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fresh_42 said:
Euler, 1753, but I don't know how he did it.
The first of many. I was thinking more on the lines of Fermat, but yes, I think Euler did it for the cubes. And the question that still remains unanswered, though many have their guesses, is whether Fermat had a proof for it.
 
Charles Link said:
and was looking for some integer examples where a3+b3=c3 .

Huh? Doesn't Wiles' Theorem (formerly Fermat's Last Theorem) say there are no such triples?
 
Vanadium 50 said:
Huh? Doesn't Wiles' Theorem (formerly Fermat's Last Theorem) say there are no such triples?
That's why I made it a thread for beginners. I wanted to see if they knew that was the case. It was intended to be semi-educational.
 
But there exists integers a, b, c and d such that [itex]a^{3}+b^{3}+c^{3}=d^{3}[/itex]. Example: [itex]3^{3}+4^{3}+5^{3}=6^{3}[/itex].
 
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There are even infinitely many solutions for ##a^3+b^3=c^3##.
 
fresh_42 said:
There are even infinitely many solutions for ##a^3+b^3=c^3##.
?
 
Svein said:
?
Read the OP carefully. All triples ##(a,0,a)##, ##(a,-a,0)## are integer solutions!
 
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  • #10
fresh_42 said:
Read the OP carefully. All triples ##(a,0,a)##, ##(a,-a,0)## are integer solutions!
Of course! I just added the Fermat condition mentally - the integers should be >0!
 
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  • #11
Svein said:
But there exists integers a, b, c and d such that [itex]a^{3}+b^{3}+c^{3}=d^{3}[/itex]. Example: [itex]3^{3}+4^{3}+5^{3}=6^{3}[/itex].
So, we know that for a^2+b^2=c^2, we can write it as:
a=m^2-n^2,b=2mn and therefore c=m^2+n^2, and then we can write it for all positive integers. Can we do the same for [itex]a^{3}+b^{3}+c^{3}=d^{3}[/itex] ??
 
  • #12
Congratulations. You got me (and others) with your trick question.

Ha.
Ha.
Ha.
 
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