4. Choose and work either a) or b), NOT BOTH. (a) Show that the function f (x) = sin z for x €R is uniformly continuous.

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Using Example in photo1, solve the same way showing sidework(rightside) and proof(leftside) of the problem in photo2

**Problem 4**

Choose and work either a) or b), NOT BOTH.

(a) Show that the function \( f(x) = \sin x \) for \( x \in \mathbb{R} \) is uniformly continuous.

(b) Show that the function \( k(x) = \sin(1/x) \) is not uniformly continuous on the set \( D(k) = \{ x \in \mathbb{R}^+ : 0 < x \} \).
Transcribed Image Text:**Problem 4** Choose and work either a) or b), NOT BOTH. (a) Show that the function \( f(x) = \sin x \) for \( x \in \mathbb{R} \) is uniformly continuous. (b) Show that the function \( k(x) = \sin(1/x) \) is not uniformly continuous on the set \( D(k) = \{ x \in \mathbb{R}^+ : 0 < x \} \).
The image contains handwritten mathematical notes related to proving the uniform continuity of a function on an interval. It deals with the function \( f(x) = \frac{1}{x} \) on the interval \([1, \infty)\).

### Content Details:

1. **Function Definition:**
   - \( f: [1, \infty) \rightarrow \mathbb{R}, \, f(x) = \frac{1}{x} \).

2. **Goal:**
   - The objective is to prove that \( f \) is uniformly continuous on \([1, \infty)\).

3. **Uniform Continuity Definition:**
   - For every \( \varepsilon > 0 \), there exists a \( \delta > 0 \) such that for all \( x, u \) in \([1, \infty)\), if \( |x-u| < \delta \), then \( |f(x) - f(u)| < \varepsilon \).

4. **Proof Structure:**
   - If \( \varepsilon > 0 \), choose \( \delta = \varepsilon \).
   - Assume \( x, u \in [1, \infty) \).

5. **Evaluation of Difference:**
   - \(|f(x) - f(u)| = \left|\frac{1}{x} - \frac{1}{u}\right|\)
   - This simplifies to:
     \[
     \left|\frac{u - x}{x \cdot u}\right|
     \]

6. **Conclusion:**
   - Based on calculations, \(|x-u| \leq \delta = \varepsilon\) ensures \(|f(x) - f(u)| < \varepsilon\).

7. **Additional Conditions:**
   - \( x \geq 1, u \geq 1 \).
   - There are bounding conditions discussed with inequalities.

### Diagram Explanation:

- The notes use colored text and underline to highlight key steps in the derivation.
- The bounding of terms like \(|x-u|\) and manipulation of \( \delta \) and \( \varepsilon \) demonstrate methods to show uniform continuity.
- The final conclusion reinforces the result that the function is indeed uniformly continuous on the specified interval.
Transcribed Image Text:The image contains handwritten mathematical notes related to proving the uniform continuity of a function on an interval. It deals with the function \( f(x) = \frac{1}{x} \) on the interval \([1, \infty)\). ### Content Details: 1. **Function Definition:** - \( f: [1, \infty) \rightarrow \mathbb{R}, \, f(x) = \frac{1}{x} \). 2. **Goal:** - The objective is to prove that \( f \) is uniformly continuous on \([1, \infty)\). 3. **Uniform Continuity Definition:** - For every \( \varepsilon > 0 \), there exists a \( \delta > 0 \) such that for all \( x, u \) in \([1, \infty)\), if \( |x-u| < \delta \), then \( |f(x) - f(u)| < \varepsilon \). 4. **Proof Structure:** - If \( \varepsilon > 0 \), choose \( \delta = \varepsilon \). - Assume \( x, u \in [1, \infty) \). 5. **Evaluation of Difference:** - \(|f(x) - f(u)| = \left|\frac{1}{x} - \frac{1}{u}\right|\) - This simplifies to: \[ \left|\frac{u - x}{x \cdot u}\right| \] 6. **Conclusion:** - Based on calculations, \(|x-u| \leq \delta = \varepsilon\) ensures \(|f(x) - f(u)| < \varepsilon\). 7. **Additional Conditions:** - \( x \geq 1, u \geq 1 \). - There are bounding conditions discussed with inequalities. ### Diagram Explanation: - The notes use colored text and underline to highlight key steps in the derivation. - The bounding of terms like \(|x-u|\) and manipulation of \( \delta \) and \( \varepsilon \) demonstrate methods to show uniform continuity. - The final conclusion reinforces the result that the function is indeed uniformly continuous on the specified interval.
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