# Basic taylor series for f(x-dx)

## Main Question or Discussion Point

Hi, how would you find the taylor series for f(x-dx). i know that substituting x-dx in the series for f(x) is not correct.

mathman
You are using an unusual terminology. Typically a Taylor series looks like:

f(a+x)=f(a) + xf'(a) + x2 f''(a)/2! + ...

When a=0, it is called a MacLaurin series.

what happens if you have dx instead of a. the second post on this website http://www.wilmott.com/messageview.cfm?catid=19&threadid=17563 [Broken]
has a formula but i dont know how it was derived.

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u are using dx in the sense of a second point of x, or a change in x
check out this page from wikiversity that breaks everything down really well.
normally i know that posts from wiki are frowned upon, but i learnt from this site and i think they break it down really rigorously and guide you nicely through the expansion of a function into a summed power series and then into taylors series at different points.
http://en.wikiversity.org/wiki/Taylor's_series

Saying "Taylor Series" is not enough, you have to attach a point around which you are expanding the function. Notice that around a different point, the taylor series will also have different coefficients.

In your example, f(x+dx) was calculated around a point x, so of course substitution won't work for the exapnasion of f(x) around 0.