statements: (a) 7152n +3. 25n-2. (b) 131 3"+2+ 42n+1. (c) 27 25n+1 + 5n+2. (d) 43 16"+2 1 72n+1

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
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Chapter1: Fundamental Concepts Of Algebra
Section1.2: Exponents And Radicals
Problem 91E
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6b .Short and simplified.
68
ELEMENTARY NUMBER THEORY
6. For n > 1, use congruence theory to establish each of the following divisibilit.
statements:
(a) 7|52m +3. 25n–2.
(b) 13|3"+2 + 42n+1.
+ 5n+2
(c) 27|25n+1
(d) 4316"+2 + 72n+1.
7. For n > 1, show that
(-13)"+1 = (-13)" +(-13)"-1 (mod 181)
[Hint: Notice that (–13)² = –13 +1 (mod 181); use induction on n.]
8. Prove the assertions below:
(a) If a is an odd integer, then a? = 1 (mod 8).
(b) For any integer a, a³ = 0, 1, or 6 (mod 7).
(c) For any integer a, a* = 0 or 1 (mod 5).
(d) If the integer a is not divisible by 2 or 3, then a² = 1 (mod 24).
9. If p is a prime satisfying n < p < 2n, show that
(:)
2n
= 0 (mod p)
10. If a1, a2,..., an is a complete set of residues modulo n and gcd(a, n) = 1, prove that
aa¡, aa2, . , aa, is also a complete set of residues modulo n.
[Hint: It suffices to show that the numbers in question are incongruent modulo n.]
11. Verify that 0, 1, 2, 2², 2³, ..., 2° form a complete set of residues modulo 11, but that
0, 12, 22, 32, .., 10² do not.
12. Prove the following statements:
(a) If gcd(a, n) = 1, then the integers
c, c+a, c+ 2a, c+ 3a, ... , c+ (n – 1)a
form a complete set of residues modulo n for any c.
(b) Any n consecutive integers form a complete set of residues modulo n.
[Hint: Use part (a).]
(c) The product of any set of n consecutive integers is divisible by n.
13. Verify that if a = b (mod n¡) and a = b (mod n2), then a = b (mod n), where the integer
n = lcm(n1, n2). Hence, whenever n¡ and n2 are relatively prime, a = b (mod ninɔ).
4. Give an example to show that a = b* (mod n) and k = j (mod n) need not imply that
a = b (mod n).
5. Establish that if a is an odd integer, then for any n > 1
20
= 1 (mod 2"+2)
[Hint: Proceed by induction on n.]
Use the theory of congruences to verify that
89|24- 1
97|248 – 1
and
Transcribed Image Text:68 ELEMENTARY NUMBER THEORY 6. For n > 1, use congruence theory to establish each of the following divisibilit. statements: (a) 7|52m +3. 25n–2. (b) 13|3"+2 + 42n+1. + 5n+2 (c) 27|25n+1 (d) 4316"+2 + 72n+1. 7. For n > 1, show that (-13)"+1 = (-13)" +(-13)"-1 (mod 181) [Hint: Notice that (–13)² = –13 +1 (mod 181); use induction on n.] 8. Prove the assertions below: (a) If a is an odd integer, then a? = 1 (mod 8). (b) For any integer a, a³ = 0, 1, or 6 (mod 7). (c) For any integer a, a* = 0 or 1 (mod 5). (d) If the integer a is not divisible by 2 or 3, then a² = 1 (mod 24). 9. If p is a prime satisfying n < p < 2n, show that (:) 2n = 0 (mod p) 10. If a1, a2,..., an is a complete set of residues modulo n and gcd(a, n) = 1, prove that aa¡, aa2, . , aa, is also a complete set of residues modulo n. [Hint: It suffices to show that the numbers in question are incongruent modulo n.] 11. Verify that 0, 1, 2, 2², 2³, ..., 2° form a complete set of residues modulo 11, but that 0, 12, 22, 32, .., 10² do not. 12. Prove the following statements: (a) If gcd(a, n) = 1, then the integers c, c+a, c+ 2a, c+ 3a, ... , c+ (n – 1)a form a complete set of residues modulo n for any c. (b) Any n consecutive integers form a complete set of residues modulo n. [Hint: Use part (a).] (c) The product of any set of n consecutive integers is divisible by n. 13. Verify that if a = b (mod n¡) and a = b (mod n2), then a = b (mod n), where the integer n = lcm(n1, n2). Hence, whenever n¡ and n2 are relatively prime, a = b (mod ninɔ). 4. Give an example to show that a = b* (mod n) and k = j (mod n) need not imply that a = b (mod n). 5. Establish that if a is an odd integer, then for any n > 1 20 = 1 (mod 2"+2) [Hint: Proceed by induction on n.] Use the theory of congruences to verify that 89|24- 1 97|248 – 1 and
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