Chapter 1: Problem 3
Prove the Distributive Laws: (a) \(A \cap(B \cup C)=(A \cap B) \cup(A \cap C)\), (b) \(A \cup(B \cap C)=(A \cup B) \cap(A \cup C)\).
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Chapter 1: Problem 3
Prove the Distributive Laws: (a) \(A \cap(B \cup C)=(A \cap B) \cup(A \cap C)\), (b) \(A \cup(B \cap C)=(A \cup B) \cap(A \cup C)\).
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Give an example of two functions \(f, g\) on \(\mathbb{R}\) to \(\mathbb{R}\) such that \(f \neq g\), but such that \(f \circ g=g \circ f\).
(a) Show that if \(f: A \rightarrow B\) is injective and \(E \subseteq A\), then \(f^{-1}(f(E))=E\). Give an example to show that equality need not hold if \(f\) is not injective. (b) Show that if \(f: A \rightarrow B\) is surjective and \(H \subseteq B\), then \(f\left(f^{-1}(H)\right)=H .\) Give an example to show that equality need not hold if \(f\) is not surjective.
Prove that \(n^{3}+(n+1)^{3}+(n+2)^{3}\) is divisible by 9 for all \(n \in \mathbb{N}\).
Show that if \(f: A \rightarrow B\) and \(G, H\) are subsets of \(B\), then \(f^{-1}(G \cup H)=f^{-1}(G) \cup f^{-1}(H)\) and \(f^{-1}(G \cap H)=f^{-1}(G) \cap f^{-1}(H)\).
Prove that \(3+11+\cdots+(8 n-5)=4 n^{2}-n\) for all \(n \in \mathbb{N}\).
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