a) Prove that for all integers n > 0, 10" = 1(mod 9). You may refer to theorems from class or the textbook.

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter1: Fundamental Concepts Of Algebra
Section1.2: Exponents And Radicals
Problem 92E
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Recall the Modular Equivalence Theorem from Chapter 8: a = b (mod d) means
that a and b have the same remainder when divided by d. Furthermore, note that if an integer n
has a remainder of zero when divided by d, then d divides n.
Let n be a positive integer. The decimal representation of n is an expression of the form
n = d,10k + dx-110"-1 + ... + d, 10' + d,10°
Where the coefficients dr, ., do are called the digits of n. The digits take on the values
0, 1,2, .,9 and the first digit d, is nonzero.
....
a) Prove that for all integers n > 0, 10" = 1(mod 9). You may refer to theorems from class or
the textbook.
b) Use part a to prove that a positive integer is divisible by 9 if and only if the sum of its digits
dy + ...+ d, is divisible by 9.
Transcribed Image Text:Recall the Modular Equivalence Theorem from Chapter 8: a = b (mod d) means that a and b have the same remainder when divided by d. Furthermore, note that if an integer n has a remainder of zero when divided by d, then d divides n. Let n be a positive integer. The decimal representation of n is an expression of the form n = d,10k + dx-110"-1 + ... + d, 10' + d,10° Where the coefficients dr, ., do are called the digits of n. The digits take on the values 0, 1,2, .,9 and the first digit d, is nonzero. .... a) Prove that for all integers n > 0, 10" = 1(mod 9). You may refer to theorems from class or the textbook. b) Use part a to prove that a positive integer is divisible by 9 if and only if the sum of its digits dy + ...+ d, is divisible by 9.
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