Bézout's identity
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In number theory, Bézout's identity, named after Étienne Bézout, is a linear diophantine equation. It states that if a and b are integers with greatest common divisor d, then there exist integers x and y such that
- ax + by = d.
Numbers x and y as above can be determined with the extended Euclidean algorithm, but they are not uniquely determined.
For example, the greatest common divisor of 12 and 42 is 6, and we can write
- 12x + 42y = 6.
with some of the solutions being
- (-3)·12 + 1·42 = 6
and also
- 4·12 + (-1)·42 = 6.
The greatest common divisor d of a and b is in fact the smallest positive integer that can be written in the form ax + by.
Bézout's identity works not only in the ring of integers, but also in any other principal ideal domain (PID). That is, if R is a PID, and a and b are elements of R, and d is a greatest common divisor of a and b, then there are elements x and y in R such that ax + by = d. The reason: the ideal Ra+Rb is principal and indeed is equal to Rd. An integral domain in which Bézout's identity holds is called a Bézout domain.
To confirm: In some credible books, this identity has been attributed to French mathematician Claude Gaspard Bachet de Méziriac.
External links
- Online calculator of Bézout's identity.
- Bezout's Identity for Gaussian Integers, Fermat's Last Theorem Blog covers topics in the history of Fermat's Last Theorem.de:Lemma von Bézout
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