Exercise 17.2.8. Define a binary relation from the given partition, and show that the relation has the above three properties. 588 CHAPTER 17 EQUIVALENCE RELATIONS AND EQUIVALENC (a) The partition in Example 17.2.3(b) (b) The partition in Example 17.2.3(c) (c) The partition in Example 17.2.3(d) (d) The partition in Example 17.2.4(b) (e) The partition in Example 17.2.4(c)

Algebra: Structure And Method, Book 1
(REV)00th Edition
ISBN:9780395977224
Author:Richard G. Brown, Mary P. Dolciani, Robert H. Sorgenfrey, William L. Cole
Publisher:Richard G. Brown, Mary P. Dolciani, Robert H. Sorgenfrey, William L. Cole
Chapter2: Working With Real Numbers
Section2.1: Basic Assumptions
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Please do Exercise 17.2.8 part C and E and please show step by step and explain

Example 17.2.3.
(a) Consider the set of real numbers R. We know that every element of R
belongs to one of two sets: the set of rational numbers, Q, or the set of
irrational numbers, I. The union of these two subsets, QUI = R, and
Q and I are disjoint sets, so based on the definition {Q, I} is a partition
of R. Alternatively the word "partition" can be used as a verb, so we
could also say that Q and I partition R.
(b) Let E and O be the even and odd integers, respectively. Then {E, O} is
a partition of Z. Alternatively we could also say that E and O partition
Z.
(c) Let S be the set of all single-element subsets of Z, so that for example
{-552}, {7}, {1492} are all elements of S. Then S is also a partition
of Z. Here S has an infinite number of elements (all the single-element
subsets of Z), but each element of S is a finite set.
(d) Consider the set of complex numbers C. Every element of C has a real
part which we denote as Re[z] (as in Chapter 2). Let Ra be the set of
all complex numbers with real part a, i.e. Ra = {z € C | Re[z] = a}.
Let P be the set consisting of all of the Ra's, i.e. P = {RaVa € R}.
Then P is a partition of C. Here P has an infinite number of elements,
where each element of P is an infinite set.
Example 17.2.4.
584CHAPTER 17 EQUIVALENCE RELATIONS AND EQUIVALENCE CLASSE
(a) When making an inventory of the animals in a zoo, we may wish to
count the number of antelopes, the number of baboons, the number of
cheetahs, and so forth. In this case, all of the animals of the same species
might be grouped together in a single set. Each species give rise t a
different set and these sets form a partition of the animals in that zoo.
(b) If we are concerned only with people's given names (what Americans
would call "first name"), we can partition any set of people according
to given name. Each set in the partition consists of all people who share
a particular given name.
(c) In geometry, sometimes we are interested only in the shape of a triangle
and not its location or orientation. In this case, we talk about congruent
triangles, where congruent means that corresponding sides of the two
triangles are equal, and corresponding angles are also equal. For any
triangle we may define the set of all triangles congruent to that triangle.
There are an infinite number of such sets which form a partition of the
set of all triangles.
Transcribed Image Text:Example 17.2.3. (a) Consider the set of real numbers R. We know that every element of R belongs to one of two sets: the set of rational numbers, Q, or the set of irrational numbers, I. The union of these two subsets, QUI = R, and Q and I are disjoint sets, so based on the definition {Q, I} is a partition of R. Alternatively the word "partition" can be used as a verb, so we could also say that Q and I partition R. (b) Let E and O be the even and odd integers, respectively. Then {E, O} is a partition of Z. Alternatively we could also say that E and O partition Z. (c) Let S be the set of all single-element subsets of Z, so that for example {-552}, {7}, {1492} are all elements of S. Then S is also a partition of Z. Here S has an infinite number of elements (all the single-element subsets of Z), but each element of S is a finite set. (d) Consider the set of complex numbers C. Every element of C has a real part which we denote as Re[z] (as in Chapter 2). Let Ra be the set of all complex numbers with real part a, i.e. Ra = {z € C | Re[z] = a}. Let P be the set consisting of all of the Ra's, i.e. P = {RaVa € R}. Then P is a partition of C. Here P has an infinite number of elements, where each element of P is an infinite set. Example 17.2.4. 584CHAPTER 17 EQUIVALENCE RELATIONS AND EQUIVALENCE CLASSE (a) When making an inventory of the animals in a zoo, we may wish to count the number of antelopes, the number of baboons, the number of cheetahs, and so forth. In this case, all of the animals of the same species might be grouped together in a single set. Each species give rise t a different set and these sets form a partition of the animals in that zoo. (b) If we are concerned only with people's given names (what Americans would call "first name"), we can partition any set of people according to given name. Each set in the partition consists of all people who share a particular given name. (c) In geometry, sometimes we are interested only in the shape of a triangle and not its location or orientation. In this case, we talk about congruent triangles, where congruent means that corresponding sides of the two triangles are equal, and corresponding angles are also equal. For any triangle we may define the set of all triangles congruent to that triangle. There are an infinite number of such sets which form a partition of the set of all triangles.
Exercise 17.2.8. Define a binary relation from the given partition, and
show that the relation has the above three properties.
588 CHAPTER 17 EQUIVALENCE RELATIONS AND EQUIVALENCE CLASSES
(a) The partition in Example 17.2.3(b)
(b) The partition in Example 17.2.3(c)
(c) The partition in Example 17.2.3(d)
(d) The partition in Example 17.2.4(b)
(e) The partition in Example 17.2.4(c)
Transcribed Image Text:Exercise 17.2.8. Define a binary relation from the given partition, and show that the relation has the above three properties. 588 CHAPTER 17 EQUIVALENCE RELATIONS AND EQUIVALENCE CLASSES (a) The partition in Example 17.2.3(b) (b) The partition in Example 17.2.3(c) (c) The partition in Example 17.2.3(d) (d) The partition in Example 17.2.4(b) (e) The partition in Example 17.2.4(c)
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