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useful lemma
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2022-08-26
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A USEFUL LEMMA
In the MATHEMATICAL REFLECTIONS
column of issue 13 of LOADSTAR we
included a nice little program which
computes the GCD of two integers by
repeated use of the Euclidean
Algorithm.
We could have gone on to say that:
LEMMA: If (A,B) represents the GCD of
the two integers A and B, then there
always exist integers C and D such
that
AC + BD = (A,B).
This result will not be proved here,
but it can be found in any text on
elementary number theory. If you FEEL
like doing it yourself, use the method
we used in issue 13 to generate the
GCD of A and B by repeated use of the
Euclidean Algorithm. Substitution from
one line to the next provides you
with the desired integers C and D.
As an example, (7,5)=1, that is the
greatest common divisor of 7 and 5 is
1. Thus there must exist integers C
and D such that
7C + 5D = 1.
Try C=3 and D=-4.
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