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Unformatted text preview: Math 220A Complex Analysis Solutions to Homework #2 Prof: Lei Ni TA: Kevin McGown Conway, Page 14, Problem 11. Parts of what follows are adapted from the text Modular Functions and Dirichlet Series in Number Theory by Tom Apostol. There are shorter proofs, but I am trying to avoid compactness arguments. Before giving the solution, we establish some notation. We will write b x c to denote the floor of a real number x ; this is defined to be the greatest integer not exceeding x . We will write { x } to denote the fractional part of x ; this is defined to be x b x c . In order to solve the problem, we will prove the following: Theorem 1 The set exp(2 in )  n Z + is dense in the unit circle if and only if is irrational. Taking arguments and normalizing by 2 , the above theorem is clearly equiva lent to the following. Theorem 2 The sequence { } , { 2 } , { 3 } ,... is dense in [0 , 1] if and only if is irrational. Proof. If is rational, then it is easy to see that {{ n }  n Z + } is a finite set and hence it cannot be dense in the unit circle. (A finite subset of C is closed and thus cannot be dense in an infinite set.) Suppose is irrational. Without loss of generality, we will assume that [0 , 1]. Indeed, one may replace by { } after making the observation that { n } = { n { }} ....
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This note was uploaded on 10/19/2009 for the course MATH 814 taught by Professor Cong during the Three '09 term at University of Adelaide.
 Three '09
 Cong
 Math, Number Theory

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