The problem consists of several parts related to set theory: listing elements of sets, finding set operations, simplifying set expressions using laws, describing sets in set-builder notation, proving set laws, representing sets using Venn diagrams, and proving a set identity. We will address questions 1, 2, 3 and 4 in this response.

Discrete MathematicsSet TheorySet OperationsSet NotationDe Morgan's LawIntersectionUnionSet Difference
2025/4/15

1. Problem Description

The problem consists of several parts related to set theory: listing elements of sets, finding set operations, simplifying set expressions using laws, describing sets in set-builder notation, proving set laws, representing sets using Venn diagrams, and proving a set identity. We will address questions 1, 2, 3 and 4 in this response.

2. Solution Steps

1(a) List the elements of the set {x: x is an integer greater than -2 but less than 9}.
The integers greater than -2 are -1, 0, 1, 2, ...
The integers less than 9 are 8, 7, 6, 5, ...
Therefore, the set is {-1, 0, 1, 2, 3, 4, 5, 6, 7, 8}.
1(b) List the elements of the set {x: x is an integer} ∩ {0, √3, π, 2i }.
The set {x: x is an integer} consists of integers.
The set {0, √3, π, 2i } consists of 0, the square root of 3, pi, and 2 times the imaginary unit i.
The intersection of these two sets consists of elements that are both integers and are in {0, √3, π, 2i }.
The only integer in {0, √3, π, 2i } is

0. Therefore, the intersection is {0}.

1(c) List the elements of the set {x² + 1: x ∈ A} where A = {-2, -1, 0, 1, 2}.
We calculate x2+1x^2 + 1 for each element xx in AA:
If x=2x = -2, then x2+1=(2)2+1=4+1=5x^2 + 1 = (-2)^2 + 1 = 4 + 1 = 5.
If x=1x = -1, then x2+1=(1)2+1=1+1=2x^2 + 1 = (-1)^2 + 1 = 1 + 1 = 2.
If x=0x = 0, then x2+1=(0)2+1=0+1=1x^2 + 1 = (0)^2 + 1 = 0 + 1 = 1.
If x=1x = 1, then x2+1=(1)2+1=1+1=2x^2 + 1 = (1)^2 + 1 = 1 + 1 = 2.
If x=2x = 2, then x2+1=(2)2+1=4+1=5x^2 + 1 = (2)^2 + 1 = 4 + 1 = 5.
The set is {5, 2, 1, 2, 5} = {1, 2, 5}.
1(d) List the elements of the set { √x + 2 : x ∈ B} where B = {-3, -4, 0, 1, 2}.
We calculate x+2\sqrt{x + 2} for each element xx in BB:
If x=3x = -3, then x+2=3+2=1\sqrt{x + 2} = \sqrt{-3 + 2} = \sqrt{-1}, which is not a real number.
If x=4x = -4, then x+2=4+2=2\sqrt{x + 2} = \sqrt{-4 + 2} = \sqrt{-2}, which is not a real number.
If x=0x = 0, then x+2=0+2=2\sqrt{x + 2} = \sqrt{0 + 2} = \sqrt{2}.
If x=1x = 1, then x+2=1+2=3\sqrt{x + 2} = \sqrt{1 + 2} = \sqrt{3}.
If x=2x = 2, then x+2=2+2=4=2\sqrt{x + 2} = \sqrt{2 + 2} = \sqrt{4} = 2.
Assuming we are looking for real numbers, the set is {√2, √3, 2}.

2. Given A = {0, 2, 4, 6, 8, 10}, B = {1, 3, 5, 7, 9}, C = {1, 2, 4, 5, 7, 8}, D = {1, 2, 3, 5, 7, 8, 9}.

(a) (A - B) - C
AB={0,2,4,6,8,10}A - B = \{0, 2, 4, 6, 8, 10\}
(AB)C={0,2,4,6,8,10}{1,2,4,5,7,8}={0,6,10}(A - B) - C = \{0, 2, 4, 6, 8, 10\} - \{1, 2, 4, 5, 7, 8\} = \{0, 6, 10\}.
(b) (A ∩ B) U (A ∩ C)
AB={}A ∩ B = \{\} (empty set, since there are no common elements)
AC={2,4,8}A ∩ C = \{2, 4, 8\}
(AB)U(AC)={}U{2,4,8}={2,4,8}(A ∩ B) U (A ∩ C) = \{\} U \{2, 4, 8\} = \{2, 4, 8\}.
(c) D ∩ (A ∩ C)
AC={2,4,8}A ∩ C = \{2, 4, 8\}
D(AC)={1,2,3,5,7,8,9}{2,4,8}={2,8}D ∩ (A ∩ C) = \{1, 2, 3, 5, 7, 8, 9\} ∩ \{2, 4, 8\} = \{2, 8\}.
(e) (A U B) - (C ∩ D)
AUB={0,1,2,3,4,5,6,7,8,9,10}A U B = \{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10\}
CD={1,2,4,5,7,8}C ∩ D = \{1, 2, 4, 5, 7, 8\}
(AUB)(CD)={0,1,2,3,4,5,6,7,8,9,10}{1,2,4,5,7,8}={0,3,6,9,10}(A U B) - (C ∩ D) = \{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10\} - \{1, 2, 4, 5, 7, 8\} = \{0, 3, 6, 9, 10\}.

3. Using the laws of sets, simplify the following

(a) [AU(BC)][A' U (B ∩ C)]'
Using De Morgan's law: (XUY)=XY(X U Y)' = X' ∩ Y'
[AU(BC)]=(A)(BC)=A(BUC)[A' U (B ∩ C)]' = (A')' ∩ (B ∩ C)' = A ∩ (B' U C') (using De Morgan's law again)
(b) (A - B) U (A ∩ B)
AB=ABA - B = A ∩ B'
(AB)U(AB)=(AB)U(AB)=A(BUB)=AU=A(A - B) U (A ∩ B) = (A ∩ B') U (A ∩ B) = A ∩ (B' U B) = A ∩ U = A, where UU is the universal set.
(c) (A - B)'
AB=ABA - B = A ∩ B'
(AB)=(AB)=AU(B)=AUB(A - B)' = (A ∩ B')' = A' U (B')' = A' U B (using De Morgan's Law)
(d) (A U B) ∩ (A U B')
(AUB)(AUB)=AU(BB)=AU{}=A(A U B) ∩ (A U B') = A U (B ∩ B') = A U \{\} = A

4. Describe each of the following in set builder notation:

(a) A = {1, 8, 27, 64, 125}
A = {x:x=n3,n{1,2,3,4,5}x: x = n^3, n \in \{1, 2, 3, 4, 5\}}
(b) B = {0, 2, 4, 6, 8, 12}
B = {x:x=2n,n{0,1,2,3,4,6}x: x = 2n, n \in \{0, 1, 2, 3, 4, 6\}}
(c) C = {1, 3, 9, 27, 81}
C = {x:x=3n,n{0,1,2,3,4}x: x = 3^n, n \in \{0, 1, 2, 3, 4\}}
(d) D = {(1,2), (2,4), (3,6), (4,8)}
D = {(x,y):y=2x,x{1,2,3,4}(x, y): y = 2x, x \in \{1, 2, 3, 4\}}

3. Final Answer

1(a) {-1, 0, 1, 2, 3, 4, 5, 6, 7, 8}
1(b) {0}
1(c) {1, 2, 5}
1(d) {√2, √3, 2}
2(a) {0, 6, 10}
2(b) {2, 4, 8}
2(c) {2, 8}
2(e) {0, 3, 6, 9, 10}
3(a) A(BUC)A ∩ (B' U C')
3(b) A
3(c) A' U B
3(d) A
4(a) {x:x=n3,n{1,2,3,4,5}x: x = n^3, n \in \{1, 2, 3, 4, 5\}}
4(b) {x:x=2n,n{0,1,2,3,4,6}x: x = 2n, n \in \{0, 1, 2, 3, 4, 6\}}
4(c) {x:x=3n,n{0,1,2,3,4}x: x = 3^n, n \in \{0, 1, 2, 3, 4\}}
4(d) {(x,y):y=2x,x{1,2,3,4}(x, y): y = 2x, x \in \{1, 2, 3, 4\}}

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