Discrete Mathematics with Applications 4th Edition

Published by Cengage Learning
ISBN 10: 0-49539-132-8
ISBN 13: 978-0-49539-132-6

Chapter 6 - Set Theory - Exercise Set 6.3 - Page 372: 11

Answer

$For\,\,all\,\,sets\,\,A,\,B,\,\,and\,C\,\,\\ if\,\,A \subseteq B\,then\,\,A \cap (B \cap C)^c = \varnothing \\ this\,\,is\,\,false:\\ counter\,\,example\,\,:\\ U=\left \{ 6,7,8,9 \right \}\\ A=\left \{ 6,7 \right \},B=\left \{ 6,7,8 \right \},C=\left \{ 8,9 \right \}\\ A\subseteq B\,\,\,(\left \{ 6,7 \right \}\subseteq \left \{ 6,7,8 \right \})\\ B\cap C=\left \{ 6,7,8 \right \}\cap \left \{ 8,9 \right \}=\left \{ 8 \right \}\\ (B\cap C)^c=\left \{ 6,7,9 \right \}\\ A \cap (B \cap C)^c=\left \{ 6,7 \right \}\cap \left \{ 6,7,9 \right \}=\left \{ 6,7 \right \}\\ \therefore A \cap (B \cap C)^c\neq \varnothing $

Work Step by Step

$For\,\,all\,\,sets\,\,A,\,B,\,\,and\,C\,\,\\ if\,\,A \subseteq B\,then\,\,A \cap (B \cap C)^c = \varnothing \\ this\,\,is\,\,not\,\,true:\\ counter\,\,example\,\,:\\ U=\left \{ 6,7,8,9 \right \}\\ A=\left \{ 6,7 \right \},B=\left \{ 6,7,8 \right \},C=\left \{ 8,9 \right \}\\ A\subseteq B\,\,\,(\left \{ 6,7 \right \}\subseteq \left \{ 6,7,8 \right \})\\ B\cap C=\left \{ 6,7,8 \right \}\cap \left \{ 8,9 \right \}=\left \{ 8 \right \}\\ (B\cap C)^c=\left \{ 6,7,9 \right \}\\ A \cap (B \cap C)^c=\left \{ 6,7 \right \}\cap \left \{ 6,7,9 \right \}=\left \{ 6,7 \right \}\\ \therefore A \cap (B \cap C)^c\neq \varnothing $
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