x-xo x-xo 12. Suppose f:D → R has a limit at xo. Prove that f:D →→ R has a limit at xo and that limxx |f(x)| = | limx→x, f(x)|. 13. Define f: RR by f(x) = r - [r) (See Example 2 6 for the definition of [x].) Determine xx0

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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Could you do 12 and 14, thanks

### Problem 12:
Suppose \( f : D \rightarrow \mathbb{R} \) has a limit at \( x_0 \). Prove that \( |f| : D \rightarrow \mathbb{R} \) has a limit at \( x_0 \) and that \(\lim_{x \rightarrow x_0} |f(x)| = |\lim_{x \rightarrow x_0} f(x)|\).

### Problem 13:
Define \( f : \mathbb{R} \rightarrow \mathbb{R} \) by \( f(x) = x - \lfloor x \rfloor \). (See Example 2.6 for the definition of \(\lfloor x \rfloor\).) Determine those points at which \( f \) has a limit, and justify your conclusions.

### Problem 14:
Define \( f : \mathbb{R} \rightarrow \mathbb{R} \) as follows:

\[
f(x) = 
\begin{cases} 
8x & \text{if } x \text{ is a rational number} \\
2x^2 + 8 & \text{if } x \text{ is an irrational number} 
\end{cases}
\]

Use sequences to guess at which points \( f \) has a limit, then use \( \epsilon \)'s and \( \delta \)'s to justify your conclusions.

### Note:
This text is aimed at helping students understand the properties of limits and how to prove them using given definitions and problem-solving techniques.
Transcribed Image Text:### Problem 12: Suppose \( f : D \rightarrow \mathbb{R} \) has a limit at \( x_0 \). Prove that \( |f| : D \rightarrow \mathbb{R} \) has a limit at \( x_0 \) and that \(\lim_{x \rightarrow x_0} |f(x)| = |\lim_{x \rightarrow x_0} f(x)|\). ### Problem 13: Define \( f : \mathbb{R} \rightarrow \mathbb{R} \) by \( f(x) = x - \lfloor x \rfloor \). (See Example 2.6 for the definition of \(\lfloor x \rfloor\).) Determine those points at which \( f \) has a limit, and justify your conclusions. ### Problem 14: Define \( f : \mathbb{R} \rightarrow \mathbb{R} \) as follows: \[ f(x) = \begin{cases} 8x & \text{if } x \text{ is a rational number} \\ 2x^2 + 8 & \text{if } x \text{ is an irrational number} \end{cases} \] Use sequences to guess at which points \( f \) has a limit, then use \( \epsilon \)'s and \( \delta \)'s to justify your conclusions. ### Note: This text is aimed at helping students understand the properties of limits and how to prove them using given definitions and problem-solving techniques.
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