When will there exist solutions to ax + (a+2)y = c?

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Homework Help Overview

The discussion revolves around the conditions under which solutions exist for the linear Diophantine equation ax + (a+2)y = c, focusing on the role of the greatest common divisor (GCD) in determining solvability.

Discussion Character

  • Conceptual clarification, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore the relationship between the GCD of a and (a+2) and the existence of solutions. Questions arise regarding the necessity of finding a specific expression for the GCD and the implications of the values of a, c, x, and y being positive integers or not.

Discussion Status

The conversation includes various attempts to clarify the conditions for solutions and the nature of the GCD. Some participants suggest that additional context about the variables is needed, while others propose exploring the implications of the GCD further. There is no explicit consensus, but several productive lines of inquiry are being pursued.

Contextual Notes

Participants note that a and b are natural numbers, while x and y are integers, with constraints on the GCD. There is uncertainty regarding the specific forms of the variables and their relationships.

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Homework Statement



When will there exist solutions to ax + (a+2)y = c?

Homework Equations



GCD

The Attempt at a Solution



Of course, this is a linear Diophantine equation. I know that a solution will exist when gcd(a, (a+2)) | c.

gcd(a, (a+2)) = d ⇒ ∃ x,y ∈ ℤ ∋ xa + y(a+2) = d

a = 0(a+2) + a
a+2 = (a) + 2
a = β(2) + r
 
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gcd(a, (a+2)) has a shorter expression.
Not sure what the last three lines are saying.
 
mfb said:
gcd(a, (a+2)) has a shorter expression.
Not sure what the last three lines are saying.

I just started the algorithm for finding the GCD, but I don't think that I actually need to find an expression.

Hm. Well, I know that a and a+2 are both odd or even depending on a.
 
Shackleford said:

Homework Statement



When will there exist solutions to ax + (a+2)y = c?

Homework Equations



GCD

The Attempt at a Solution



Of course, this is a linear Diophantine equation. I know that a solution will exist when gcd(a, (a+2)) | c.

gcd(a, (a+2)) = d ⇒ ∃ x,y ∈ ℤ ∋ xa + y(a+2) = d

a = 0(a+2) + a
a+2 = (a) + 2
a = β(2) + r

Have you forgotten to tell us whether or not a, c, x, y are positive (non-negative?) integers?
 
Ray Vickson said:
Have you forgotten to tell us whether or not a, c, x, y are positive (non-negative?) integers?

Partially. a, b ∈ ℕ and x, y ∈ ℤ and 1 ≤ d ≤ min{a,b}.
 
If you want to solve mu+nv = d when m and n are relatively prime, you should be able to find a specific solution with Bezout theorem. With that specific solution, you should be able to find a general solution (u,v) without too much difficulty.

The thing is that ax +(a+2) y = c has not that form, or at least not always. Why ? Mfb gave you a good hint. Think about it
 
Shackleford said:
I just started the algorithm for finding the GCD, but I don't think that I actually need to find an expression.
I think you should, as the final expression is very easy. It is a bit like leaving 4+5 in a final answer. It is not wrong in terms of mathematics, but you should replace it by 9.
 

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