Find 100th Derivative of f(x) = x/(1+x^2) at 1

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Homework Help Overview

The problem involves finding the 100th derivative of the function f(x) = x/(1+x^2) at the point x=1. The context is centered around derivatives and power series representation.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss using power series for |x| < 1, but express concerns about its applicability at x=1. There are attempts to compute derivatives directly, which some find complicated. Questions arise regarding the nature of the derivatives, particularly whether higher-order derivatives might be zero.

Discussion Status

Multiple approaches are being explored, including power series and partial fraction decomposition. Some participants are questioning the assumptions about the behavior of derivatives at the specified point, and hints have been offered to consider alternative methods.

Contextual Notes

There is mention of the function being a fraction and the potential complexity of derivatives at x=1. The discussion reflects uncertainty about the convergence of series and the implications of using partial fractions.

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Homework Statement


Find the 100th derivative at 1 of f(x) = x/(1+x^2)


Homework Equations





The Attempt at a Solution


For |x| < 1 I can write f as a power series (since 1/(1+x^2) = sum_n (-1)^n x^(2n)) but this won't work at 1. I tried writing out the first few derivatives at 1 explicitly but things got pretty messy. Any ideas?
 
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Maybe I'm missing something but since this is a second-order equation, aren't all derivatives past the second one zero?
 
Fleem, it is a fraction.

Hint: split it in partial fractions.
 
Count Iblis said:
Fleem, it is a fraction.

Hint: split it in partial fractions.

I need glasses.
 
eok20 said:

The Attempt at a Solution


For |x| < 1 I can write f as a power series (since 1/(1+x^2) = sum_n (-1)^n x^(2n)) but this won't work at 1. I tried writing out the first few derivatives at 1 explicitly but things got pretty messy. Any ideas?

Are you just trying to find the derivative at one point? If so, and you are trying to find the derivative at the point x=1, then why not do the power series at about x=1. If you use partial fractions as another poster suggested, the roots will be +/=i so I think the series should converge
 

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