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Where $F:R^n \rightarrow R$, $a=(a^1,...,a^\mu)$ and $x=(x^1,...,x^\mu)$.

Also, $H_\mu (a)=\frac{\partial F}{\partial x^\mu}|_{x=a}$

Hi there, this is a problem on General Relativity from Robert Wald. I'm trying to solve it for a few hours but still, it doesn't look that difficult.. I'm pretty sure the fundamental theorem of calculus is a good start:

$F(x)-F(a)=∫_{a}^{x}F′(s)ds$

Then , with $ s=t(x-a)+a$ we have

$F(x)-F(a)=(x-a)∫_{0}^{1}F′[t(x-a)+a]dt$

Which bares a nice similarity! But I don't know how to generalize from there. I was checking up on Stokes theorem to see if there's any connection.

Every time I get stuck on a problem for more than one hour I know it must be something obvious. Weird.

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    Thanks! :) Yesyerday I had none, today I have two solutions :P2011-05-22

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I'm sorry for my ignorance, maybe I'm not getting something, but.. isn't it just the Taylor expansion of a function, up to the fist order?