iv. Use iii. to prove that the set P of all polynomials with integer coefficients is denumerable (Hint: use that P = UPn and Theorem 1.3.12). v. Use iv. and the fact that a polynomial of degree n has at most n real roots to show that the set of algebraic numbers is denumerable.

Elements Of Modern Algebra
8th Edition
ISBN:9781285463230
Author:Gilbert, Linda, Jimmie
Publisher:Gilbert, Linda, Jimmie
Chapter8: Polynomials
Section8.4: Zeros Of A Polynomial
Problem 22E
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Can you answer only part 4 and part 5
The following problem is designed for you to prove that the set of all (real) algebraic numbers is denumerable. A
number x* E R is an algebraic number if it is a root of a polynomial with integer coefficients, that is p(x*)= 0
where
p(x) = anx" + an-1x"- + ..+ a1x + ao,
for x E R
for some a; E Z for i = 1, 2, . .. , n, and some n E N.
i. Show that if A is a denumerable set then A x Z is denumerable as well (Hint: you may find simpler to
prove that A × N is denumerable first).
ii. Use i. to show that forn € N, the set
Z x Z x . .. x Z,
n times
is denumerable (Hint: try by induction).
iii. Use ii. to prove that for each n E N the set Pn, defined as
Pn :=
{All polynomials with integer coefficients of degree <n },
is denumerable.
iv. Use iii. to prove that the set P of all polynomials with integer coefficients is denumerable (Hint: use that
P = U Pn and Theorem 1.3.12).
v. Use iv. and the fact that a polynomial of degree n has at most n real roots to show that the set of algebraic
numbers is denumerable.
Transcribed Image Text:The following problem is designed for you to prove that the set of all (real) algebraic numbers is denumerable. A number x* E R is an algebraic number if it is a root of a polynomial with integer coefficients, that is p(x*)= 0 where p(x) = anx" + an-1x"- + ..+ a1x + ao, for x E R for some a; E Z for i = 1, 2, . .. , n, and some n E N. i. Show that if A is a denumerable set then A x Z is denumerable as well (Hint: you may find simpler to prove that A × N is denumerable first). ii. Use i. to show that forn € N, the set Z x Z x . .. x Z, n times is denumerable (Hint: try by induction). iii. Use ii. to prove that for each n E N the set Pn, defined as Pn := {All polynomials with integer coefficients of degree <n }, is denumerable. iv. Use iii. to prove that the set P of all polynomials with integer coefficients is denumerable (Hint: use that P = U Pn and Theorem 1.3.12). v. Use iv. and the fact that a polynomial of degree n has at most n real roots to show that the set of algebraic numbers is denumerable.
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