Suppose that f: R→ R is a function. Suppose that there exists a constant c< 1 so that for all x, y E R we have f(x) = f(y)| < cx - y. Prove that f is continuous on R.

Advanced Engineering Mathematics
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ISBN:9780470458365
Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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**Problem Statement:**

Suppose that \( f: \mathbb{R} \to \mathbb{R} \) is a function. Suppose that there exists a constant \( c < 1 \) so that for all \( x, y \in \mathbb{R} \) we have \( |f(x) - f(y)| < c|x - y| \). Prove that \( f \) is continuous on \( \mathbb{R} \).
Transcribed Image Text:**Problem Statement:** Suppose that \( f: \mathbb{R} \to \mathbb{R} \) is a function. Suppose that there exists a constant \( c < 1 \) so that for all \( x, y \in \mathbb{R} \) we have \( |f(x) - f(y)| < c|x - y| \). Prove that \( f \) is continuous on \( \mathbb{R} \).
**Theorem 4.3.2 (Characterizations of Continuity)**

Let \( f : A \to \mathbb{R} \), and let \( c \in A \). The function \( f \) is continuous at \( c \) if and only if any one of the following three conditions is met:

(i) For all \( \epsilon > 0 \), there exists a \( \delta > 0 \) such that \( |x - c| < \delta \) (and \( x \in A \)) implies \( |f(x) - f(c)| < \epsilon \);

(ii) For all \( V_{\epsilon}(f(c)) \), there exists a \( V_{\delta}(c) \) with the property that \( x \in V_{\delta}(c) \) (and \( x \in A \)) implies \( f(x) \in V_{\epsilon}(f(c)) \);

(iii) For all \( (x_n) \to c \) (with \( x_n \in A \)), it follows that \( f(x_n) \to f(c) \).

If \( c \) is a limit point of \( A \), then the above conditions are equivalent to

(iv) \(\lim_{x \to c} f(x) = f(c)\).
Transcribed Image Text:**Theorem 4.3.2 (Characterizations of Continuity)** Let \( f : A \to \mathbb{R} \), and let \( c \in A \). The function \( f \) is continuous at \( c \) if and only if any one of the following three conditions is met: (i) For all \( \epsilon > 0 \), there exists a \( \delta > 0 \) such that \( |x - c| < \delta \) (and \( x \in A \)) implies \( |f(x) - f(c)| < \epsilon \); (ii) For all \( V_{\epsilon}(f(c)) \), there exists a \( V_{\delta}(c) \) with the property that \( x \in V_{\delta}(c) \) (and \( x \in A \)) implies \( f(x) \in V_{\epsilon}(f(c)) \); (iii) For all \( (x_n) \to c \) (with \( x_n \in A \)), it follows that \( f(x_n) \to f(c) \). If \( c \) is a limit point of \( A \), then the above conditions are equivalent to (iv) \(\lim_{x \to c} f(x) = f(c)\).
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