home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
Loadstar 12
/
012.d81
/
number theory
< prev
next >
Wrap
Text File
|
2022-08-26
|
2KB
|
156 lines
NUMBER THEORY
Elementary number theory is one of the
easiest to understand fields of mathe-
matics. Like Euclidean Geometry, it
is easy to state the problems and has
a simple set of axioms and
definitions.
Although we will touch only a fraction
of the material in number theory, it
is our hope that you will pursue it
further through the literature.
Beginning with Peano's postulates
which describe the natural numbers,
1,2,3..., etc., we can develop the
entire real number system.
The concepts of mathematical induction
and well-ordering, or the actual
development of the number system will
not be covered here.
We will discuss divisibility.
DEFINITION: Let A and B be integers.
Then we say that A divides B if there
exists an integer C such that
AC = B.
We also say that B is divisible by A.
THEOREM: Let A and B be integers. If
A divides B, and if D is any integer,
then A divides BD.
PROOF: Since A divides B, there is an
integer C such that
(1) AC = B
multiplying both sides by D,
(2) ACD = BD.
Since CD is an integer and
A(CD) = BD,
the definition of 'A divides BD' is
satisfied.
THEOREM: Let A, B, and C be integers
and suppose that
(1) A + B = C.
If D is any integer which divides any
two of A, B, and C then it divides the
remaining integer.
PROOF: To start, let's assume that D
divides both A and B. We must show
that D also divides C.
Since D divides both A and B, there
exist integers E and F such that
A = DE and B = DF. Substituting these
values in equation (1) we get
(2) DE + DF = C.
By the distributive property
(factoring) we see that
(3) D(E + F) = C
Thus D divides C (since E + F is an
integer).
The other cases are handled by
reducing them to the case we just did.
For example, suppose D divides A and
C. We must show that D divides B.
Add -B-C to both sides of equation (1)
(4) A + B + (-B-C) = C + (-B-C)
(5) A + (-C) = -B
Now since D divides A and C, it also
divides A and -C. From the above
case, D must divide -B. Hence D
divides B.
For further reading I suggest the
following books:
ELEMENTARY THEORY OF NUMBERS
by Harriet Griffin
(McGraw Hill)
INTRODUCTION TO MODERN ALGEBRA AND
ANALYSIS
by Croud and Walker
(Hold, Reinhart and Winston)
A SURVEY OF MODERN ALGEBRA
by Rirkhoff and MacLine
(MacMillan)
--------------------------------------