1. Ler f : R →R be continuous. If f(c) > 0, prove there exists a neighborhood N of c such that f(N) > 0. 2. Let f : R → R and E C R. Prove ƒ is continuous iff f(E) is closed whenever E CR is closed.

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I need help with #1 and #2. Thank you

1. **Problem:** Let \( f : \mathbb{R} \to \mathbb{R} \) be continuous. If \( f(c) > 0 \), prove there exists a neighborhood \( N \) of \( c \) such that \( f(N) > 0 \).

2. **Problem:** Let \( f : \mathbb{R} \to \mathbb{R} \) and \( E \subseteq \mathbb{R} \). Prove \( f \) is continuous if and only if \( f^{-1}(E) \) is closed whenever \( E \subseteq \mathbb{R} \) is closed.

3. **Problem:** Let \( f, g : D \to \mathbb{R} \) be continuous at \( c \in D \). Prove that \( fg \) is continuous at \( c \).

4. **Definition:** A set \( X \subseteq \mathbb{R} \) is said to be disconnected if there exist disjoint open sets \( U \) and \( V \) such that \( X \subseteq U \cup V \), \( X \cap U \neq \emptyset \), and \( X \cap V \neq \emptyset \). A set is said to be connected if it is not disconnected.

   Let \( f : \mathbb{R} \to \mathbb{R} \) and \( X \subseteq \mathbb{R} \) be connected. Prove \( f(X) \) is connected.

5. **Problem:** Suppose \( f : [a, b] \to [a, b] \) is continuous. Prove there exists \( c \in [a, b] \) such that \( f(c) = c \).
   (Hint: Consider the function \( g(x) = f(x) - x \).)
Transcribed Image Text:1. **Problem:** Let \( f : \mathbb{R} \to \mathbb{R} \) be continuous. If \( f(c) > 0 \), prove there exists a neighborhood \( N \) of \( c \) such that \( f(N) > 0 \). 2. **Problem:** Let \( f : \mathbb{R} \to \mathbb{R} \) and \( E \subseteq \mathbb{R} \). Prove \( f \) is continuous if and only if \( f^{-1}(E) \) is closed whenever \( E \subseteq \mathbb{R} \) is closed. 3. **Problem:** Let \( f, g : D \to \mathbb{R} \) be continuous at \( c \in D \). Prove that \( fg \) is continuous at \( c \). 4. **Definition:** A set \( X \subseteq \mathbb{R} \) is said to be disconnected if there exist disjoint open sets \( U \) and \( V \) such that \( X \subseteq U \cup V \), \( X \cap U \neq \emptyset \), and \( X \cap V \neq \emptyset \). A set is said to be connected if it is not disconnected. Let \( f : \mathbb{R} \to \mathbb{R} \) and \( X \subseteq \mathbb{R} \) be connected. Prove \( f(X) \) is connected. 5. **Problem:** Suppose \( f : [a, b] \to [a, b] \) is continuous. Prove there exists \( c \in [a, b] \) such that \( f(c) = c \). (Hint: Consider the function \( g(x) = f(x) - x \).)
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