Chapter 1: Problem 1
If \(A\) and \(B\) are sets, show that \(A \subseteq B\) if and only if \(A \cap B=A\).
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Chapter 1: Problem 1
If \(A\) and \(B\) are sets, show that \(A \subseteq B\) if and only if \(A \cap B=A\).
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(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 \(2^{n}
Show that the function \(f\) defined by \(f(x):=x / \sqrt{x^{2}+1}, x \in
\mathbb{R}\), is a bijection of \(\mathbb{R}\) onto \(\\{y:-1
Prove that a set \(T_{1}\) is denumerable if and only if there is a bijection from \(T_{1}\) onto a denumerable set \(T_{2}\).
Prove that \(1 / \sqrt{1}+1 / \sqrt{2}+\cdots+1 / \sqrt{n}>\sqrt{n}\) for all \(n \in \mathbb{N}\).
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