Generalize Theorem 1.3.9 by proving that every rational solution of a polyno- mial equation x" + an-1a"-1 + + a1x + = 0, | with integer coefficients ak, is an integer solution.

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
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Chapter4: Polynomial And Rational Functions
Section4.2: Properties Of Division
Problem 51E
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12. Generalize Theorem 1.3.9 by proving that every rational solution of a polyno-
mial equation
-1x"-1
+ «1x + a• = 0,
+...
with integer coefficients a k,
is an integer solution.
Transcribed Image Text:12. Generalize Theorem 1.3.9 by proving that every rational solution of a polyno- mial equation -1x"-1 + «1x + a• = 0, +... with integer coefficients a k, is an integer solution.
Theorem 1.3.9. If k is an integer and the equation x = k has a rational solution,
then that solution is actually an integer.
Proof. Suppose r is a ratiomal number such that r2 = k. Let r =
as a fraction in which n and m have no common factors. Then,
er expressed
2
n
k
and so n? = m²k.
m
This equationm implies that m divides n2. However, if m 7 1, then m can be
expressed as a product of primes, and each of these primes must also divide n2.
However, if a prime number divides n2, it must also divide n (Exercise 1.3.14).
Thus, each prime factor of m divides n. Since n and m have no common factors,
this is impossible. We conclude that m =
1 and, hence, that r = n is an integer.
Transcribed Image Text:Theorem 1.3.9. If k is an integer and the equation x = k has a rational solution, then that solution is actually an integer. Proof. Suppose r is a ratiomal number such that r2 = k. Let r = as a fraction in which n and m have no common factors. Then, er expressed 2 n k and so n? = m²k. m This equationm implies that m divides n2. However, if m 7 1, then m can be expressed as a product of primes, and each of these primes must also divide n2. However, if a prime number divides n2, it must also divide n (Exercise 1.3.14). Thus, each prime factor of m divides n. Since n and m have no common factors, this is impossible. We conclude that m = 1 and, hence, that r = n is an integer.
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