MATH 110 Introduction to Number Theory Winter 2023 Homework 7
Hello, dear friend, you can consult us at any time if you have any questions, add WeChat: daixieit
Homework 7 (due Mar. 12)
MATH 110 | Introduction to Number Theory | Winter 2023
Problem 1 (20 pts). Find all natural representatives x modulo 63 such that x2 ≡ 22 (mod 63).
Hint. Use Chinese Remainder theorem [Lecture Note, Lecture 19].
Problem 2 (20 pts). Find all roots of the polynomial x3 + x + 1 modulo 27. Write your answer in natural representatives modulo 27.
Hint. Use Hensel’s lifting [Lecture Note, Lecture 20].
Problem 3. In what follows, we fix a prime number p. For n an integer, recall that vp(n) is the exponent of p appearing in the prime factorization of n. Namely, pvp(n) | n, while pvp(n)+1 ∤ n. Extend this definition to nonzero fractions as follows:
n
m
(a) (2 pts) Show that, if the two fractions and represent the same rational number, then vp() = vp().
Hence, we obtain a function vp : Q× → Z. (Recall that Q× consists of nonzero rational numbers). The p-adic norm of a rational number x is defined to be
|x|p:=
For example,
, 24 , 1 , 24 , 1 , 24 ,
, 25 ,2 = 8 , , 25 ,3 = 3 , , 25 ,5 = 25.
(b) (3 pts) Prove that |−x|p = |x|p, and |xy|p = |x|p|y|p .
(c) (5 pts) Prove the ultrametric triangle inequality
|x + y|p≤ max{ |x|p , |y|p }.
Remark. Note that max{ |x|p , |y|p} ⩽ |x|p+ |y|p . Hence, the ultrametric triangle inequality
implies the usual triangle inequality. The previous two says that | · |p can be viewed as analogy of the usual Euclidean norm of vectors, or the absolute value of real numbers.
2023-03-13