Advanced Engineering Mathematics
Advanced Engineering Mathematics
10th Edition
ISBN: 9780470458365
Author: Erwin Kreyszig
Publisher: Wiley, John & Sons, Incorporated
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Looking at photo1, can you prove the circled function {f.g} - Continue and explain with the starting HINT on photo2 in detail

### Combinations of Continuous Functions

For a subset \(D \subseteq \mathbb{R}^p\),

**Theorem:**
Let \( f, g: D \rightarrow \mathbb{R}^q \) be continuous at \( a \in \mathbb{R}^p \).

Then:

1. \( f + g, f - g, cf, fg \) are continuous at \( a \).

   Additionally, \( \frac{f}{g} \) is continuous at \( a \) provided \( g(a) \neq 0 \).

2. If \( f \) is continuous at \( a \) and \( g \) is continuous at \( b = f(a) \), then \( g \circ f \) is continuous at \( a \).
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Transcribed Image Text:### Combinations of Continuous Functions For a subset \(D \subseteq \mathbb{R}^p\), **Theorem:** Let \( f, g: D \rightarrow \mathbb{R}^q \) be continuous at \( a \in \mathbb{R}^p \). Then: 1. \( f + g, f - g, cf, fg \) are continuous at \( a \). Additionally, \( \frac{f}{g} \) is continuous at \( a \) provided \( g(a) \neq 0 \). 2. If \( f \) is continuous at \( a \) and \( g \) is continuous at \( b = f(a) \), then \( g \circ f \) is continuous at \( a \).
### Continuity of Product of Continuous Functions

This blackboard contains a proof related to the continuity of the product of two functions. Here is a transcription and explanation of the content:

1. **Definitions and Assumptions:**
   - Functions \( f, g \) with domain \( D \subset \mathbb{R}^p \) are continuous, where \( a \in \mathbb{R}^p \).
   - The focus is on proving that \( f \cdot g \) is continuous at \( a \).

2. **Proof Structure:**
   - **Continuity Condition:** For \( f \) and \( g \) to be continuous at \( a \):
     - Given \( \varepsilon > 0 \), there exists \( \delta_1 > 0 \) such that for all \( x \in \mathbb{R} \), if \( \| x - a \| < \delta_1 \), then \( \| f(x) - f(a) \| < \varepsilon \).
     - Similarly, there is \( \delta_2 > 0 \) such that \( \| g(x) - g(a) \| < \varepsilon \).
   - **Combined Condition:** Choose \( \delta = \min(\delta_1, \delta_2) \). Thus, if \( \| x - a \| < \delta \), both continuity conditions are satisfied.

3. **Mathematical Expression:**
   - Shown centrally is a bound expression for the product of \( f \) and \( g \):
     \[
     \| f(x) \cdot g(x) - f(a) \cdot g(a) \|
     \]
   - This expression expands using properties of modulus and distribution:
     \[
     = \| (f(x) - f(a)) \cdot g(a) + f(x) \cdot (g(x) - g(a)) \|
     \]
   - Further breaking down:
     \[
     = \| (f(x) - f(a)) \cdot g(a) \| + \| f(x) \cdot (g(x) - g(a)) \|
     \]

This proof demonstrates that if \( f \) and \( g \) are continuous at a point \( a \), then their product \( f \cdot g \
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Transcribed Image Text:### Continuity of Product of Continuous Functions This blackboard contains a proof related to the continuity of the product of two functions. Here is a transcription and explanation of the content: 1. **Definitions and Assumptions:** - Functions \( f, g \) with domain \( D \subset \mathbb{R}^p \) are continuous, where \( a \in \mathbb{R}^p \). - The focus is on proving that \( f \cdot g \) is continuous at \( a \). 2. **Proof Structure:** - **Continuity Condition:** For \( f \) and \( g \) to be continuous at \( a \): - Given \( \varepsilon > 0 \), there exists \( \delta_1 > 0 \) such that for all \( x \in \mathbb{R} \), if \( \| x - a \| < \delta_1 \), then \( \| f(x) - f(a) \| < \varepsilon \). - Similarly, there is \( \delta_2 > 0 \) such that \( \| g(x) - g(a) \| < \varepsilon \). - **Combined Condition:** Choose \( \delta = \min(\delta_1, \delta_2) \). Thus, if \( \| x - a \| < \delta \), both continuity conditions are satisfied. 3. **Mathematical Expression:** - Shown centrally is a bound expression for the product of \( f \) and \( g \): \[ \| f(x) \cdot g(x) - f(a) \cdot g(a) \| \] - This expression expands using properties of modulus and distribution: \[ = \| (f(x) - f(a)) \cdot g(a) + f(x) \cdot (g(x) - g(a)) \| \] - Further breaking down: \[ = \| (f(x) - f(a)) \cdot g(a) \| + \| f(x) \cdot (g(x) - g(a)) \| \] This proof demonstrates that if \( f \) and \( g \) are continuous at a point \( a \), then their product \( f \cdot g \
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