F(z) limit using formal definition

  • Thread starter Thread starter Meggle
  • Start date Start date
  • Tags Tags
    Definition Limit
Click For Summary
SUMMARY

The discussion focuses on evaluating the limit of the function f(z) = |z|²/z as z approaches 0 using the formal definition of a limit. The user demonstrates that along the real axis, f(z) approaches 0, and similarly along the imaginary axis, f(z) also approaches 0. The conclusion drawn is that the limit lim z→0 f(z) = 0, contingent upon establishing the relationship between epsilon and delta. The user seeks clarification on how to simplify the delta expression to finalize the proof.

PREREQUISITES
  • Understanding of complex functions and limits
  • Familiarity with the formal definition of a limit in calculus
  • Knowledge of epsilon-delta proofs
  • Basic algebraic manipulation of complex numbers
NEXT STEPS
  • Study epsilon-delta definitions of limits in calculus
  • Learn about complex analysis, specifically limits of complex functions
  • Explore techniques for simplifying expressions involving limits
  • Practice problems involving limits of functions as they approach singularities
USEFUL FOR

Students in calculus or complex analysis courses, educators teaching limit concepts, and anyone seeking to understand the formal definition of limits in the context of complex functions.

Meggle
Messages
16
Reaction score
0

Homework Statement


For each of the following choices of f(z) use the definition of a limit to obtain lim z-->0 f(z) or prove that the limit doesn't exist
(a) [tex]\frac{|z|^{2}}{z}[/tex]

Homework Equations


Formal limit definition

The Attempt at a Solution


f(z) = [tex]\frac{|z|^{2}}{z}[/tex]
f(z) = [tex]\frac{x^{2} + y^{2}}{x +iy}[/tex]
So if z=(x,0), f(z)=[tex]\frac{x^{2} + 0}{x +i0}[/tex] = x
Then f(z) --> 0 as (x,y) --> 0 along the real axis
And if z=(0,y), f(z)=[tex]\frac{0 + y^{2}}{0 +iy}[/tex] = [tex]\frac{y}{i}[/tex]
Then f(z) --> 0 as (x,y) --> 0 along the imaginary axis
So maybe lim z-->0 f(z)= 0
Suppose lim z-->0 f(z)= 0, then for each [tex]\epsilon[/tex] >0 there exists [tex]\delta[/tex] >0 such that 0 < |z - 0| < [tex]\delta[/tex] implies |f(z) - 0| < [tex]\epsilon[/tex]
...
Sooooo how do I figure delta out of that? I can't see how to simplify it or what to do next. It's due tomorrow, of course. :smile: And there's a (b) and a (c) , but think I could work them out if I could finish this one.

Also, can anyone tell me how to make the formulas update? I've changed all the SUP to curly brackets and carrots, but it won't seem to referesh. Edit never mind, seems they just don't show right on preview.
 
Last edited:
Physics news on Phys.org
Here's a suggestion:
[tex]\left| \frac{z}{|z|} \right| = 1[/tex]
So if you write
[tex]|f(z)| = \left| |z| \cdot \left( \frac{z}{|z|} \right)^{-1} \right|[/tex]
you can work in your delta.
 
Epsilon= delta. Try to justify it.
 

Similar threads

Replies
8
Views
2K
  • · Replies 17 ·
Replies
17
Views
4K
Replies
6
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
Replies
2
Views
2K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 13 ·
Replies
13
Views
4K