1.1 set and set operations (math 17)
DESCRIPTION
For freshman taking Math 17. c/o UP.TRANSCRIPT
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Chapter 1
Algebra of Numbers
MATH 17. COLLEGE ALGEBRA AND TRIGONOMETRY
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1. Sets and Set Operations 2. The Set of Real Numbers 3. Operations on Real Numbers and Laws of
Exponents 4. The Set of Complex Numbers 5. Operations on and Factoring of Polynomials/
Zeros of Polynomials 6. Rational Expressions and Radicals 7. Equations 8. Inequalities
Chapter Outline
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Chapter 1
Section 1.1
Sets, Set Operations,
and Number Sets
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Section Objectives
Describe sets using different
methods
Identify different set relations and
perform different set operations
Identify special
number sets
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Set has pervaded almost all of mathematics so that it has become a fundamental concept. It becomes impossible to define set precisely in terms of more basic concepts.
Notion of a Set
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A set is a well-defined collection of objects.
It should be possible to determine (in some
manner) whether an object belongs to the given
collection or not.
Notion of a Set
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Example
The collection of all natural numbers between 0 and 5.
Which of the following collection of objects are sets?
SET
The collection of all buildings in UPLB.
SET
The collection of all schools near Intramuros.
NOT A SET
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Example
The collection of all handsome students in this class.
Which of the following collection of objects are sets?
NOT A SET
The collection of all flying horses.
SET
The collection of all letters in the word honorificabilitudinitatibus.
SET
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Definition
If an object belongs to a set, it is called an element of the set.
𝑎 ∈ 𝐴: 𝑎 is an element of the set 𝐴
Element
Otherwise, the object is not an element of the set.
𝑎 ∉ 𝐴: 𝑎 is not an element of the set 𝐴
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Example
ℎ ∈ 𝐴 𝑞 ∉ 𝐴
If 𝐴 is the set of all letters in the word “Philippines”, then
3 ∈ 𝑂 22 ∉ 𝑂
If 𝑂 is the set of all odd integers, then
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Roster/Enumeration method
Set is indicated by enumerating the elements of the set and enclosing them in a pair of braces.
Rule method
Set is indicated by enclosing in a pair of braces a
phrase describing the elements of the set with the
condition that those objects, and only those, which
have the described property belong to the set.
Describing a Set
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Example
using the roster method, 𝐴 = 𝑚, 𝑎, 𝑡, ℎ, 𝑒, 𝑖, 𝑐, 𝑠
while using the rule method,
𝐴 = distinct letters of the word "mathematics"
If 𝐴 is the collection of distinct letters in the word mathematics, then
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Set Builder Notation
The set-builder notation is another way of
describing sets using the rule method. This method
uses a defining property of the elements.
𝑥 𝑥 𝑖𝑠 𝑎 __________ is read as "the set of all x such
that x is a (a certain defining property of all the
elements)”.
Describing a Set
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Example
𝐵 = counting number from 1 to 5 or
𝐵 = 𝑥 x is a counting number from 1 to 5 or
𝐵 = 𝑦 𝑦 is a counting number less than 6
If 𝐵 = 1,2,3,4,5 , write 𝐵 using the rule method.
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Example
IMPRACTICAL and DIFFICULT
If 𝐶 = clock, blue, television , write 𝐶 using the rule method.
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Example
IMPOSSIBLE
If 𝐷 = points in the line 𝑥 = 2 , write 𝐷 using the roster method.
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Time to Think!
When is the use of the rule method appropriate? The roster method?
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The concept and the representation of the collection is subject to the following: • the collection must be well-defined • each unique object of the set should be
uniquely represented; and • the order of representing each object of the
set is immaterial.
Remember
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Definition
- denoted by ∅ or { }
- are sets having no elements
Empty Sets
Example: 𝐷 = y y is a country in Asia with no people
= ∅ 𝐴 = {positive numbers less than − 5} = { }
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Empty Set is a subset of any set.
Empty Set
∅ ⊆ 𝐴, for any set 𝐴.
The empty set is a subset of itself.
∅ ⊆ ∅
Remarks:
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Definition
Otherwise, the set is said to be infinite.
Finite/Infinite Sets
Loosely speaking, we say a set is finite if it is possible to write down completely in a list all the elements of the set or if its elements can be counted (and the counting process terminates)
Sets differ in sizes and kinds.
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Example
The set of all rational numbers between 0 and 5.
Which of the following sets is finite? Infinite?
INFINITE
The set of all buildings in UPLB.
FINITE
The set of all flying horses. FINITE
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Example
The set of all hair strands on your head FINITE
The set of points in a circle.
INFINITE
The set of counting numbers between 1 and 1,000,000,000 FINITE
The set of grains of sand in a beach FINITE
Which of the following sets is finite? Infinite?
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Definition
Cardinality
The cardinality (or size) of a set is the number of elements of that set.
𝑛 𝐴 : the cardinality of set 𝐴
Example: 1. If 𝐴 is the set of vowels in the English alphabet then
𝑛 𝐴 =
2. n ∅ = 0
5.
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Definition
Set of all elements under consideration
Universal Set
Superset of all sets under consideration
Denoted by 𝑈
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Example
If 𝐴 = 𝑥 𝑥 is an even counting number 𝐵 = 𝑦 𝑦 is an odd counting number 𝐶 = 𝑧 𝑧 is a prime number
A possible universal set is
𝑈 = 𝑥 𝑥 is a counting number OR
𝑈 = 𝑦 𝑦 is an integer OR
𝑈 = 𝑧 𝑧 is a real number
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Two sets 𝐴 and 𝐵 are equal if they have exactly the same elements.
𝐴 = 𝐵: Set 𝐴 is equal to set 𝐵.
Equal Sets
Otherwise, the sets are not equal.
𝐴 ≠ 𝐵:Set 𝐴 is not equal to set 𝐵.
Definition
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To say 𝐴 ≠ 𝐵, we should be able to produce an element that is in 𝐴 but not in 𝐵 or an element that is in 𝐵 but not in 𝐴.
Equal Sets
Thus, to say 𝐴 = 𝐵, we should be certain that every element in 𝐴 belongs to 𝐵 and every element in 𝐵 is also in 𝐴.
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Example
𝐴 = 𝐵
If 𝐴 is the set of all letters in the word “resistance”, and 𝐵 is the set of all letters in the word “ancestries”, then
𝐵 ≠ 𝐶 because 𝑖 ∈ 𝐵 but 𝑖 ∉ 𝐶.
If 𝐶 is the set of all letters in the word “ancestor”, then
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Time to Think!
If 𝐴 = {2, 3, 5, 7, 11} and 𝐵 = {x|x is a prime number less than 12}
Is 𝐴 = 𝐵?
If C= {11, 2, 5, 7, 3}
Is 𝐴 = 𝐶?
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Definition
We write 𝐴 ⊆ 𝐵 if and only if 𝑥 ∈ 𝐴 implies 𝑥 ∈ 𝐵.
Subsets and Supersets
𝐴 ⊆ 𝐵: Set 𝐴 is a subset of 𝐵 or Set 𝐵 is a superset of 𝐴
Set 𝐴 is said to be a subset of set 𝐵 if every element of 𝐴 is also an element of 𝐵.
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Thus, if there is an element in 𝐴 which is not in 𝐵,
we say 𝐴 is not a subset of 𝐵 and we write 𝐴 ⊈ 𝐵.
Subset of a Set
If 𝐴 ⊆ 𝐵 then whenever 𝑥 is in 𝐴, 𝑥 is also in 𝐵.
and
If whenever 𝑥 is in 𝐴, 𝑥 is also in 𝐵 then 𝐴 ⊆ 𝐵
This notation is to be understood to mean two
things:
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Example
If 𝐵 = 1, 2, 3, 4 then
𝐵 ⊈ 1,2, 5, 6 .
If 𝐶 = 𝑎, 𝑏, 𝑐, 𝑑 and 𝐷 = 𝑎, 𝑏, 𝑐
Yes it is.
but
𝐵 ⊆ {1, 2, 3, 4, 5}
• Is 𝐷 ⊆ C?
No it isn’t. Thus 𝐶 ⊈ 𝐷.
• Is 𝐶 ⊆ 𝐷?
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Time to Think!
• If 𝐴 ⊆ 𝐵 and 𝐵 ⊆ 𝐴, what can be said about 𝐴 and 𝐵?
• If 𝐴 ⊆ 𝐵 and 𝐵 ⊆ 𝐶, is 𝐴 ⊆ 𝐶?
• Is 𝐴 ⊆ 𝐴?
• Give an example for sets 𝐴 and 𝐵 such that 𝐴 ⊆ 𝐵 but 𝐵 ⊈ 𝐴
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If 𝐴 ⊆ 𝐵 and 𝐵 ⊆ 𝐶 then 𝐴 ⊆ 𝐶.
Subset of a Set
Transitive Property of Set Inclusion
𝐴 ⊆ 𝐴, for any set 𝐴.
Reflexive Property of Set Inclusion
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Definition
𝐴 ⊂ 𝐵 if and only if A is a nonempty set and 𝐴 ⊆ 𝐵 but 𝐵 ≠ 𝐴.
Proper Subsets “⊂’’
If 𝐴 ⊆ 𝐵 and 𝐵 ⊆ 𝐴 then 𝐴 = 𝐵.
Alternative Definition of Equality of Sets
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Example
If 𝐶 = 𝑎, 𝑏, 𝑐, 𝑑 and 𝐷 = 𝑎, 𝑏, 𝑐
Therefore 𝐷 ⊂ C.
𝐶 ⊈ 𝐷 since 𝑑 ∈ 𝐶 but 𝑑 ∉ 𝐷.
𝐷 ⊆ C and
Is 𝐷 ⊂ C?
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Definition
Two sets 𝐴 and 𝐵 are in one-to-one correspondence if it is possible to pair each element of 𝐴 with exactly one element of 𝐵 and each element of 𝐵 with exactly one element of 𝐴.
One-to-one Correspondence
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Example
Is there a one-to-one correspondence between the set of days in a week and the set of colors in the rainbow?
YES
M T W Th F Sa S
red orange yellow green blue indigo violet
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Example
Is there a one-to-one correspondence between the set of days in a week and the set of months in a year? NO
Jan
Feb
Mar
Ap
r
May
Jun
Jul
Au
g
Sep
Oct
No
v
Dec
S M T W Th F Sa
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Example
Let 𝐴 = 1,2,3,4 𝐵 = 3,6,9,12 𝐶 = −4, −3, −2, −1,1,2,3,4
NO
Is there a one-to-one correspondence between set 𝐴 and set 𝐶?
YES
Is there a one-to-one correspondence between set 𝐴 and set 𝐵?
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Example
Is there a one-to-one correspondence between the set of even counting numbers and the set of odd counting numbers?
YES
E 2 4 6 8 34290
…
O 1 3 5 7 34289
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Time to Think!
Is there a one-to-one correspondence between the set of points in a line and the
set of all counting numbers?
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Definition
Two sets are equivalent (or of the same size) if they are in one-to-one correspondence.
Equivalent Sets
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Time to Think!
• When are two sets “not equivalent”?
• If 𝐴 and 𝐵 are equivalent and 𝐵 and 𝐶 are equivalent, are 𝐴 and 𝐶 equivalent?
• Are equivalent sets equal?
• Are equal sets equivalent?
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Number Sets
ℕ = set of natural (counting) numbers ={1,2,3, … }
𝕎 = set of whole numbers = {0,1,2,3, … }
ℤ = set of integers = {… , −3, −2, −1,0,1,2,3, … }
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Number Sets
N- = set of negative counting numbers E = set of even integers
O = set of odd integers
E+ = set of positive even integers
E- = set of negative even integers
P = set of prime numbers C = set of composite numbers
𝑘ℤ= set of multiples of k, k is positive
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Example
2ℤ = … , −6, −4, −2,0,2,4,6, …
3ℤ = … , −9, −6, −3,0,3,6,9, …
4ℤ = … , −12, −8, −4,0,4,8,12, …
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Venn Diagram
𝐴 ⊆ 𝐵 𝐵 ⊆ 𝐴
𝐴
𝐵 𝐴
𝐵
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Example
Draw a Venn Diagram such that A is not a subset of B.
𝐴 𝐵
𝐴
𝐵 or
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Example
Draw a Venn Diagram satisfying 𝐴 ⊆ 𝐵, 𝐴 ⊆ 𝐶 and 𝐵 ⊆ 𝐶.
𝐴
𝐵
𝐶
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Definition
Two sets are disjoint if they have no element in common.
Disjoint Sets
𝐴 and 𝐵 are disjoint:
If 𝑥 ∈ 𝐴 then 𝑥 ∉ 𝐵.
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Disjoint Sets
𝐴
𝐵
𝐴
𝐵
𝐴 and 𝐵 are disjoint 𝐴 and 𝐵 are not disjoint
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Definition
Union The union of two sets 𝐴 and 𝐵 is the set of elements that belong to 𝐴 or to 𝐵.
𝐴 ∪ 𝐵: 𝐴 union B
UA B
𝐴 ∪ 𝐵 = 𝑥 𝑥 ∈ 𝐴 or 𝑥 ∈ 𝐵
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Example
If 𝐴 = 1,3,5 and 𝐵 = 𝑎, 𝑏, 𝑐 then 𝐴 ∪ 𝐵 = 1, 3, 5, 𝑎, 𝑏, 𝑐
Moreover, 𝑛 𝐴 = 3, 𝑛 𝐵 = 3 and
𝑛 𝐴 ∪ 𝐵 = 6
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Time to Think!
Is it always true that 𝑛 𝐴 ∪ 𝐵 = 𝑛 𝐴 + 𝑛 𝐵 ?
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Definition
Intersection
The intersection of two sets 𝐴 and 𝐵 is the set of elements that belong to 𝐴 and to 𝐵.
𝐴 ∩ 𝐵: 𝐴 intersection B
𝐴 ∩ 𝐵 = 𝑥 𝑥 ∈ 𝐴 and 𝑥 ∈ 𝐵
UA B
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Example
If 𝐴 = 𝑎, 𝑒, 𝑖, 𝑜, 𝑢 and 𝐵 = 𝑎, 𝑏, 𝑐, 𝑑, 𝑒 then 𝐴 ∩ 𝐵 = 𝑎, 𝑒
If 𝑃 is the set of all prime numbers and 𝐶 is the set of all composite numbers, then
𝑃 ∩ 𝐶 = ∅
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Definition
Alternative Definition
Two sets 𝐴 and 𝐵 are disjoint if and only if 𝐴 ∩ 𝐵 = ∅.
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Cardinality of 𝐴 ∪ 𝐵
If 𝐴 and 𝐵 are disjoint 𝑛 𝐴 ∪ 𝐵 = 𝑛 𝐴 + 𝑛 𝐵
In general, 𝑛 𝐴 ∪ 𝐵 = 𝑛 𝐴 + 𝑛 𝐵 − 𝑛 𝐴 ∩ 𝐵
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Example
If 𝐺 = 1,3,5,7,9,10 and 𝐻 = 3,6,9,12 , then
𝑛 𝐺 = 6 𝑛 𝐻 = 4
𝑛 𝐺 ∩ 𝐻 = 2
𝑛 𝐺 ∪ 𝐻 = 8
Then
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Definition
Set Difference
𝐴 𝐵
A-B= 𝑥 𝑥 ∈ 𝐴, 𝑥 ∉ 𝐵
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Definition
Set Difference A-B= 𝑥 𝑥 ∈ 𝐴, 𝑥 ∉ 𝐵
A= {1,2,3,4,5,6} B= {2,5,7,9,10}
{1, 2, 3, 4, 5, 6}
{2, 5, 7, 9, 10}
A−B =
B−A =
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Definition
The complement of 𝐴 denoted by 𝐴′, is the set of all elements of 𝑈 that are not in 𝐴.
Complement
𝑈 𝐴
𝐴′ = 𝑥 𝑥 ∈ 𝑈, 𝑥 ∉ 𝐴
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Example
If 𝑈 = 1,3,5,7,9 and A = 5, 9 then
𝑈 𝐴
5 9 1
7
3
𝐴′ = 1,3,7
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Complement of a Set
𝑈′ =
∅′ =
Remark:
𝐴′ = 𝑈 − 𝐴
∅
𝑈
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Complement of a Set
U U
𝐴′ ′ = 𝐴
𝐴′ 𝐴′ ′
𝐴 𝐴
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Example
UA B
A B 'A B
Illustrate using the Venn diagrams
𝐴 ∪ 𝐵 ′
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Example
Illustrate using the Venn diagrams
𝐴′ ∩ 𝐵′
UA B
'A
UA B
'B
' 'A B
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Example
'A B ' 'A B
' ' 'A B A B
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Definition
Cross Product
The cross product (or Cartesian product) of two sets 𝐴 and 𝐵 is the set of all possible ordered pairs 𝑥, 𝑦 where 𝑥 ∈ 𝐴 and 𝑦 ∈ 𝐵.
𝐴 × 𝐵: 𝑥, 𝑦 𝑥 ∈ 𝐴 and 𝑦 ∈ 𝐵
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Example
If 𝐴 = 1,2 and 𝐵 = 𝑎, 𝑏
On the other hand 𝐵 × 𝐴 = 𝑎, 1 , 𝑎, 2 , 𝑏, 1 , 𝑏, 2
then 𝐴 × 𝐵 = 1, 𝑎 , 1, 𝑏 , 2, 𝑎 , 2, 𝑏
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Time to Think!
What is the cardinality of 𝐴 × 𝐵?
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Definition
Power Set
The power set of any set, denoted by ℘ 𝐴 , is the set of all subsets of set 𝐴.
Let 𝐴 = 𝑎, 3, # , then ℘ 𝐴 =
𝑎 , 3 , # , 𝑎, 3 , 𝑎, # , 3, # , 𝐴, ∅
What is 𝑛 ℘ 𝐴 ? 8
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Time to Think!
What is the cardinality of the power set of any set 𝐴?
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Time to Think!
Let 𝑈 be a universal set and A ⊆ 𝑈
𝐴 ∪ 𝑈
𝐴 ∪ 𝐴′
𝐴 ∪ ∅
𝐴 ∩ 𝑈
𝐴 ∩ 𝐴′
𝐴 ∩ ∅
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Time to Think!
Let U = ℤ. Find the following:
1. ℕ ∪ 𝕎 = 𝕎 2. ℕ ∩ 𝕎= ℕ 3. 𝐸 ∪ 𝑂 = ℤ 4. 𝐸+ ′ = {0}
∪O ∪ 𝐸− 5. 3ℤ ∪ 2ℤ
6. 3ℤ ∩ 2ℤ= 6ℤ 7. ℕ′ ∩ 𝕎 = {0} 8. ℕ ∪ 𝑃′ = ℤ 9. 𝐶 ∩ 𝑃 × 𝐸− ={} 10. ℤ′ = {}
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Example
If 𝑛 𝑈 = 𝑟 and 𝑛 𝐵 = 𝑗, then 𝑛 𝐵′ =
𝑟 − 𝑗
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Example
Illustrate using the Venn diagrams
𝐴 ∩ 𝐵 ∪ 𝐶
B C A A B C
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Example
Illustrate using the Venn diagrams 𝐴 ∩ 𝐵 ∪ 𝐴 ∩ 𝐶
UA B
C
A B
UA B
C
A C
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Example
A B A C A B C
A B C A B A C