Question 1: Let R be the set of real numbers and let 2R be the set...
Prove that a disjoint union of any finite set and any countably infinite set is countably infinite. Proof: Suppose A is any finite set, B is any countably infinite set, and A and B are disjoint. By definition of disjoint, A ∩ B = ∅ Then h is one-to-one because f and g are one-to one and A ∩ B = 0. Further, h is onto because f and g are onto and given any element x in A ∪...
Problem 3: Let f(x) be a function on the set of real numbers r > 1. Define the function g(x) for x by 1 g(s)-Σf(r/n). 1<nsr Prove that f(s) -Σμ(n)g (r/n). = 1nsz Here is the Möbius function
Define four sets of integers Let P {0, 1), let Q {-11, 1, 5) , and Let R and S be arbitrary nonempty subsets of Z. Define an even indicator function F F: ZP by F(x) = (x + 1) mod 2 for x e Z That is, F(x) 1 if x is even, and F(x) = 0 if x is odd. or neither? Explain. a) Is F: Q P one-to-one, onto, both, or neither? Explain. b) Is F: (Pn...
1. a) Let A = {2n|n ∈ ℤ} (ie, A is the set of even numbers) and define function f: ℝ → {0,1}, where f(x) = XA(x) That is, f is the characteristic function of set A; it maps elements of the domain that are in set A (ie, those that are even integers) to 1 and all other elements of the domain to 0. By demonstrating a counter-example, show that the function f is not injective (not one-to-one). b)...
Let AC (0,1) be the set of real numbers with a decimal expansion containing only Os, 2s, and 5s. For example, 2/9 = 0.222... € A and 0.2500525... E A, but 1/8 = 0.125 € A. Prove that A is uncountable. Let A = {a,b,c,r,s.t} be a set with 6 distinct elements. Either construct a binary operation f: AxA+A with the property that for every 2 EA, fía, 2) = 2, f(1, ) = , and f(0, 2) = 2,...
1. Let ơ E Aut(R), where R denotes the field of real numbers. a) Prove that if a > b then σ(a) > σ(b) ( . (b) Prove that o is a continuous function. (c) Prove that ơ must be the identity function. Therefore Aut(R)-(1). (see problem 7 on pg. 567 for more details for each step). 1. Let ơ E Aut(R), where R denotes the field of real numbers. a) Prove that if a > b then σ(a) >...
5. Let R denote the set of real numbers. Which of the following subsets of R xR can be written as Ax B for appropriate subsets A, B of R? In case of a positive answer, specify the sets A and B. (a) {(z,y)12z<3, 1<y< 2}, (b) {z,)2+y= 1), (c) {(z,y)|z= 2, y R), (d) {(z,y)|z,yS 0}, (e) {(z,y) z y is an integer).
Question 2: Let R* be the group of positive real numbers under multiplication. Si that the mapping f(x) = x is an automorphism of R* . (An automorphism is a: isomorphism from a group onto itself).
Let F be the set of all real-valued functions having as domain the set R of all real numbers. Example 2.7 defined the binary operations +- and oon F. In Exercises 29 through 35, either prove the given statement or give a counterexample. 29. Function addition + on F is associative. 30. Function subtraction - on is commutative
x+3 2x Define f(x) for all real numbers x = 0. Is f a one-to-one function? Prove or give a counterexample. (Note that the write-up of the proof or counterexample should only have a few of sentences.) If the co-domain is all real numbers not equal to 1, is f an onto function? Why or why not? (Note this problem does not require a full proof or formal counterexample, just an explanation.)