Can All Linear Diophantine Equations Be Solved?

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Discussion Overview

The discussion revolves around the solvability of various linear Diophantine equations, specifically examining conditions under which integer solutions exist. Participants analyze specific equations and explore methods for determining their solvability, including the use of greatest common divisors (gcd) and modular arithmetic.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • Some participants assert that if \(a\) and \(b\) are relatively prime, then \(ax + by = N\) has integer solutions for any integer \(N\), suggesting that statement (a) is true.
  • One participant calculates \(\gcd(70, 42) = 14\) and concludes that for equation (b), since 14 does not divide 1409, there are no integer solutions.
  • In contrast, the same participant states that for equation (c), since 14 divides 1428, there are integer solutions.
  • For equation (d), it is noted that \(\gcd(2016, 4031) = 1\) which divides the right-hand side, indicating that integer solutions exist.
  • Another participant echoes the previous claims about equations (b), (c), and (d), reinforcing the conclusions drawn about their solvability.
  • Participants inquire about quicker methods for solving these equations, with one suggesting the use of modular arithmetic, particularly noting that for equation (b), the left-hand side is even while the right-hand side is odd, which implies no solutions.

Areas of Agreement / Disagreement

Participants generally agree on the analysis of equations (b), (c), and (d), but there is no explicit consensus on the validity of statement (a) as some participants have not confirmed their agreement. The discussion remains open regarding the quickest methods for solving these types of equations.

Contextual Notes

Participants rely on the properties of gcd and modular arithmetic, but the discussion does not resolve the broader implications of these methods or their applicability to all linear Diophantine equations.

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Decide which of the following equations are true or false. If false, explain/provide a counterexample.

(a) If $a, b \in \mathbb{Z}$ are relatively prime, then $ax+by = N$ has integer solutions for any integer $N$.
(b) The equation $70x+42y = 1409$ has integer solutions
(c) The equation $70x+42y = 1428$ has integer solutions
(d) The equation $2016x+4031y = 2014201520162017$ has integer solutions.

I think (a) is true since relativity prime means $\gcd(a, b) = 1$ and $1|N$.
 
Last edited:
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(b) $\gcd(70, 42) = 14$ which does not divide the RHS, so it has integer no solutions.
(c) $\gcd(70, 42) = 14$ which divides the RHS, so it has integer solutions.
(d) $\gcd(2016,4031) = 1$ which clearly divides the RHS so it has integer solutions.

Could someone please verify whether this is correct?
 
Last edited:
Guest said:
(b) $\gcd(70, 42) = 14$ which does not divide the RHS, so it has integer no solutions.
(c) $\gcd(70, 42) = 14$ which divides the RHS, so it has integer solutions.
(d) $\gcd(2016,4031) = 1$ which clearly divides the RHS so it has integer solutions.

Could someone please verify whether this is correct?

all including for (a) specified in 1st post correct
 
kaliprasad said:
all including for (a) specified in 1st post correct
Thanks. Is there a quicker way to do these questions, perhaps using something like modular arithmetic?
 
Guest said:
Thanks. Is there a quicker way to do these questions, perhaps using something like modular arithmetic?

(b) can be done quicker, for instance mod 2.
More specifically, the left hand side is even, while the right hand side is odd.
 

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