Taylor Expansion where the derivatives are undefined?

In summary, the conversation discusses how to expand the polynomial x/(x-1) at a=1. The book provides an expansion, but does not explain the process. The attempted solution uses the Mclaurin expansion, but the derivatives are undefined. The conversation also raises the possibility of using a Laurent expansion instead of a Taylor expansion. The confusion lies in the method used to derive the expansion and the fact that the function is undefined at x=1.
  • #1
pandaBee
23
0

Homework Statement


Expand x/(x-1) at a=1
The book already gives the expansion but it doesn't explain the process. The expansion it gives is:
x/(x-1) = (1+x-1)/(x-1) = (x-1)^(-1) + 1

Homework Equations


The Attempt at a Solution


I've already solved for the Mclaurin expansion for the same polynomial which gives me -x - x^2 - x^3 - x^4 - ...
The derivatives all have a power of (x-1) as its denominator therefore all of its derivatives are undefined. I don't know any other way to expand polynomials other than term by term, I've been staring at

x/(x-1) = (1+x-1)/(x-1) = (x-1)^(-1) + 1

But it doesn't make sense. All they did was just split the fraction up into two parts.
 
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  • #2
Are you sure you don't want the Laurent expansion instead of the Taylor expansion?
 
  • #3
micromass said:
Are you sure you don't want the Laurent expansion instead of the Taylor expansion?

Sorry about that, yes I believe that is the case.
 
  • #4
Are you confused about how (x-1)-1 + 1 is a Laurent series?
 
  • #5
Office_Shredder said:
Are you confused about how (x-1)-1 + 1 is a Laurent series?

I'm confused about the method used to derive it. As in I don't understand the method of the reasoning behind it.

Also I don't see how they can come up with that answer when the function x/(x-1) is undefined around x=1.
 

FAQ: Taylor Expansion where the derivatives are undefined?

What is a Taylor Expansion?

A Taylor Expansion is a mathematical method for approximating a function using a series of polynomials. It is commonly used in calculus to find the values of a function at a specific point based on its derivatives at that point.

How are derivatives used in a Taylor Expansion?

Derivatives are used in a Taylor Expansion to calculate the coefficients of the polynomials in the series. These coefficients represent the rate of change of the function at a specific point and are used to approximate the function at that point.

What does it mean for a derivative to be undefined in a Taylor Expansion?

If a derivative is undefined, it means that the function is not differentiable at that point. This could be due to a discontinuity, a sharp corner, or a point where the function is not defined.

Can a Taylor Expansion still be used if the derivatives are undefined?

Yes, a Taylor Expansion can still be used if the derivatives are undefined. However, the accuracy of the approximation may be affected. If the derivatives are undefined at the point of expansion, the Taylor Series may not converge or may have a larger error.

How can we handle undefined derivatives in a Taylor Expansion?

One way to handle undefined derivatives in a Taylor Expansion is to use a different approximation method, such as a Maclaurin Series. Another approach is to use a piecewise function, where different Taylor Series are used for different intervals of the function. Additionally, in some cases, the function itself can be manipulated to make the derivatives defined at the point of expansion.

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