MAT1348 Assignment 2 Discrete Mathematics for Computing
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Discrete Mathematics for Computing
MAT1348 Assignment 2
due: Thursday, March 9 by 11:30 pm
Q1a. [3 points] Given a proof by contradiction of the following theorem.
If the sum of S = a1 + a2 + ··· + an is an odd integer, and all the terms
a1 ,a2 , ··· ,an are odd integers, then n is odd integer.
Only the following results are supposed to be known, and anything else must be proved.
The sum of two odd integer is even. The Sum of an even integer and an odd integer is odd. The sum of number of even integer is even .
Q1b. [3 points] Let S = {a,b,c,d}. Define relation From S to S, given as subsets of S × S, What kind
relation? Circle all relations
(a) R1 : {(a,a), (d,d)}:
Circle Reflexive Symmetric Transitive
(b) R2 : {(a,a), (b,b), (c,c), (d,d), (a,b), (b,c), (a,c)}:
Circle Reflexive Symmetric Transitive
(c) R3 : {(a,a), (b,b), (c,c), (d,d), (a,b), (b,a), (b,c), (c,b)}:
Circle Reflexive Symmetric Transitive
Q2. [6 points] Let A and B be subsets of the universal set 八. Prove the following theorem
Theorem
(A ∪ B) ⊆ B
尸 使
P
If and only if
A ⊆ (A ∩ B) .
尸 使
Q
IMPORTANT! For each step in your proof, make sure it is clear whether it is an assumption, something you are about to prove, or something that follows from a previous step or definition.
Proof P → Q in other words if (A ∪ B) ⊆ B, then A ⊆ (A ∩ B). |
Proof Q → P , in other words : If A ⊆ (A ∩ B), then (A ∪ B) ⊆ B . |
Q3. [4 points] Given the following function
g : R+ × R → R × R defined g(x,y) = (3x + 2y,x2 )
determine whether or not it is injective , surjective? Fully justify your answers.
Check g(x) is injective or not. |
Check g(x) is surjective or not. |
Q4.a [2 points] Assume A and B are subsets of some universal set 八 . Complete the following member-
ship table and briefly explain how we can conclude from it that the following equation is a set
identity:
(A − B) ∪ (B ∪ C) = (A ∪ C) ∩ B
Q4.b [2 points]using the Laws from the Table of Important Set Identities. You may use one or two laws at each step, and you must write the name of the law(s) used at each step. Do not combine more than two laws in one step. Do not omit necessary parentheses.
(BONUS) [+2 bonus points] Circle the best answer for each question. You do not need to show any justification for
this, but you will only earn the bonus points if all of your answers are correct.
i. For any sets A and B, is the following claim always true, or can it sometimes be false?
Claim: If (A − B) ⊆ (B − A), then A ⊆ B . Circle: always true sometimes false
Claim: If A,B are finite set and A ⊂ B, then |A| < |B|. Circle: always true sometimes false
Claim: A × (B ∪ C) = A × (B ∪ C). Circle: always true sometimes false
ii. Let h : R − {1} = {x : x ∈ R, and x 1} → R be the function given by h(x) = .
Is h injective?
Is h surjective?
Circle:
Circle:
yes
yes
no
no
Table of Points for marking purposes. Do not write in this table.
|
Q1 |
Q2 |
Q3 |
Q4 |
BONUS |
TOTAL |
max points possible |
6 pts |
6 pts |
4 pts |
4 pts |
+2 pts |
20 points |
points obtained |
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2023-03-13