Solving Removable Singularity in [z^(c-1)]/[exp(z)-1] at z=0

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In summary, the function [z^(c-1)]/[exp(z)-1] has a removable singularity at z=0 if and only if Re(c) > 1. This can be shown by determining the order of the pole for 1/(exp(z)-1) and considering the limit. However, some cases may require the use of L'Hopital's rule. For example, when c=3/2, the function is of the indeterminate form of 0/0 at z=0, but after applying L'Hopital's rule multiple times, it approaches infinity. This means that the function is not continuous at z=0 and therefore does not have a removable singularity at that point.
  • #1
eyesontheball1
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How exactly would one show that [z^(c-1)]/[exp(z)-1]has a removable singularity at z=0? I tried using the methods introduced in my complex analysis book, but nothing seemed to work. Thanks!
 
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  • #2
That will depend on c.
You can determine the order of the pole for 1/(exp(z)-1) and then see what happens with the numerator.
Alternatively, you can just consider the limit.
 
  • #3
I'm reading that [z^(c-1)]/[exp(z)-1] has a removable singularity at z = 0 whenever Re(c) > 1, but if c = 3/2, then Re(c) > 1, and [z^(c-1)]/[exp(z)-1] = [z^(1/2)]/[exp(z)-1], which is of the indeterminate form of 0/0 at z=0, but then after applying L'Hopital's rule, this gives (1/2)[z^(-1/2)]/[exp(z)], which approaches infinity as z approaches 0. Then every subsequent application of L'Hopital's rule results in the same limit of infinity. How can it then be the case that this function has a removable singularity at z=0 when c = 3/2? My understanding was that removable singularities are removable precisely because after applying L'Hopital's rule a finite number of times, a finite limit is eventually reached, meaning the function is essentially analytic at the singularity. I'm not too familiar with complex analysis and I just started reading from my text and noticed this problem, which I haven't been able to completely understand. It's kind of an unique example compared to the rest of the examples given in my book. Can you please elaborate on this in detail?
 
  • #4
[z^(1/2)]/[exp(z)-1] is not even continuous if you ignore z=0, clearly it cannot be continuous including z=0.
 
  • #5
A removable singularity for f(z) at z=0 means that z*f(z) is finite and defined. Thus, we must check (z*z^(c-1))/[exp(z)-1] = z^c/(exp(z)-1) at z=0. Using L'Hôpital, we get c*z^(c-1)/exp(z) = 0/1 (as long as Re(c) > 1). If c=1, the numerator is 1 for all z and the singularity is not removable
 

Related to Solving Removable Singularity in [z^(c-1)]/[exp(z)-1] at z=0

1. What is a removable singularity in the context of solving [z^(c-1)]/[exp(z)-1] at z=0?

A removable singularity is a point in a function where the function is undefined, but it can be removed or "filled in" to make the function continuous. In the case of [z^(c-1)]/[exp(z)-1] at z=0, the singularity is removable because the function is undefined at z=0 due to the denominator being zero, but it can be rewritten as z^(c-1)/z= z^(c-2), which is defined at z=0.

2. Why is it important to solve for the removable singularity in [z^(c-1)]/[exp(z)-1] at z=0?

Solving for the removable singularity at z=0 is important because it allows us to extend the function to be continuous at that point. This is useful in many mathematical applications, as well as in physics and engineering problems.

3. What are the steps involved in solving for the removable singularity in [z^(c-1)]/[exp(z)-1] at z=0?

The steps involved in solving for the removable singularity at z=0 in [z^(c-1)]/[exp(z)-1] are:
1. Rewrite the function as z^(c-2)
2. Use L'Hopital's rule to evaluate the limit as z approaches 0
3. Simplify the resulting expression
4. Evaluate the limit as z approaches 0 again
5. The resulting value is the value of the removable singularity at z=0.

4. Can the removable singularity in [z^(c-1)]/[exp(z)-1] at z=0 be solved using other methods besides L'Hopital's rule?

Yes, the removable singularity at z=0 can also be solved using Taylor series expansion, which involves representing the function as an infinite sum of polynomial terms. The singularity can then be "filled in" by taking the limit of the resulting polynomial as z approaches 0.

5. Are there any real-world applications for solving the removable singularity in [z^(c-1)]/[exp(z)-1] at z=0?

Yes, there are many real-world applications for solving the removable singularity at z=0. For example, in physics and engineering, this concept is used in solving problems related to electricity and magnetism, fluid dynamics, and heat transfer. It is also used in various mathematical applications, such as in the study of complex numbers and in solving differential equations.

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