Discrete Mathematics and Its Applications, Seventh Edition

Published by McGraw-Hill Education
ISBN 10: 0073383090
ISBN 13: 978-0-07338-309-5

Chapter 2 - Section 2.2 - Set Operations - Exercises - Page 137: 57

Answer

a)$A\cup B$={$a,b,c,d,e,g,p,t,v$} b)$A\cap B$={$b,c,d$} c)$(A\cup D)\cap (B \cup C)$={$b,c,d,e,i,o,t,u,x,y$} d)$A\cup B\cup C\cup D$={$a,b,c,d,e,g,h,i,n,o,p,t,u,v,x,y,z$}

Work Step by Step

Given : A = {a, b, c, d, e}, B = {b, c, d, g, p, t, v}, C = {c, e, i, o, u, x, y, z}, and D = {d, e, h, i, n, o, t, u, x, y}. If the $i$th bit in the string is 1, then the $i$th letter of the alphabet is in the set. If the $i$th bit in the string is 0, then the $i$th letter of the alphabet is NOT in the set. The alphabet contains 26 letters, thus each string needs to contain 26 bits. A: 11111 00000 00000 00000 00000 0 B: 01110 01000 00000 10001 01000 0 C: 00101 00010 00001 00000 10011 1 D: 00011 00110 00011 00001 10011 0 a) Union: $A \cup B$: All elements that are either in A or in B If either string contains a 1 on the $i$th bit, then $A \cup B$ contains a 1 on the $i$th bit as well. $A\cup B$:11111 01000 00000 10001 01000 0 This string then corresponds to the set: $A\cup B$={$a,b,c,d,e,g,p,t,v$} b) Intersection:$A \cap B$: All elements that are both in A AND B If both strings contains a 1 on the $i$th bit, then $A \cap B$ contains a 1 on the $i$th bit as well. $A\cap B$:01110 00000 00000 00000 00000 0 This string then corresponds to the set: $A\cap B$={$b,c,d$} c) If either string contains a 1 on the $i$th bit, then union contains a 1 on the $i$th bit as well. $A\cup D$:11111 00110 00011 00001 10011 0 $B\cup C$: 01111 01010 00001 10001 11011 1 If both strings contains a 1 on the $i$th bit, then intersection contains a 1 on the $i$th bit as well. $(A\cup D)\cap (B \cup C)$:01111 00010 00001 00001 10011 0 This string then corresponds to the set: $(A\cup D)\cap (B \cup C)$={$b,c,d,e,i,o,t,u,x,y$} d)If either string contains a 1 on the $i$th bit, then union contains a 1 on the $i$th bit as well. $A\cup D$:11111 00110 00011 00001 10011 0 $B\cup C$: 01111 01010 00001 10001 11011 1 Since the union of commutative:$A\cup B\cup C\cup D=(A\cup D)\cup (B \cup C)$ $A\cup B\cup C\cup D$:11111 01110 00011 10001 11011 1 This string then corresponds to the set: $A\cup B\cup C\cup D$={$a,b,c,d,e,g,h,i,n,o,p,t,u,v,x,y,z$}
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