Number Theory. If d=gcd(a,b,c) then d is a linear combination of a,b, and c

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SUMMARY

The discussion centers on the proof that if d = gcd(a, b, c), then d can be expressed as a linear combination of a, b, and c, specifically in the form d = sa + tb + uc for some integers s, t, and u. The participants noted that while this has been established for two numbers, i.e., d = gcd(a, b), the proof for three numbers requires further exploration. The relationship gcd(a, b, c) = gcd(gcd(a, b), c) is highlighted as a potential approach to extend the proof to three variables.

PREREQUISITES
  • Understanding of the greatest common divisor (gcd) concept
  • Familiarity with linear combinations of integers
  • Knowledge of the properties of gcd involving multiple variables
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study the proof of gcd(a, b) as a linear combination of a and b
  • Explore the properties of gcd with three variables in depth
  • Learn about the Extended Euclidean Algorithm for multiple integers
  • Investigate applications of gcd in number theory and cryptography
USEFUL FOR

Students of number theory, mathematicians interested in gcd properties, and educators teaching linear combinations and their applications in algebra.

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Homework Statement


Several of us claimed that if d=gcd(a,b,c) then d is a linear combination of a,b and c, i.e. that d=sa+tb+uc for some integers s,t, and u. That is true, but we only proved the analogous claim for the greatest common divisor of two numbers, i.e. when d=gcd(a,b). We need three.



Homework Equations


N/A?



The Attempt at a Solution


I know that gcd(a,b,c)=gcd(gcd(a,b)c). Can I use this to prove? If so, I'm not sure how.
 
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Sure. If you know that gcd(x, y)= px+ qy, then gcd(gcd(a,b), c)= p(gcd(a,b))+ qc.
And gcd(a, b)= sa+ tb so gcd(gcd(a,b), c)= p(sa+ tb)+ qc= (ps)a+ (pt)b+ qc and ps, pt, and q are integers.
 

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