On Mon, 16 Nov 2009 13:51:11 +0100, Invisible <voi### [at] devnull> wrote:
>
> Oh, I did Google it. I just didn't comprehend the answer. (In  
> particular, I've already read the Wikipedia entry.)

What is so difficult to understand about it? I thought function  
composition would be one of the areas of math that you were actually good  
at, given your fanatical obsession with a certain functional programming  
language.

Anyway:

The derivative of f( g(x) ) is f'(g(x))*g'(x).

Substitute the inner function into the derivative of the outer function,  
and then multiply by the derivative of the inner function.



In your example, we want the derivative of f(f(x)) (i.e. the outer and  
inner functions are the same), and we know that f'(x) = g(x) (try not to  
mix up all the f's and g's).

df(f(x))/dx = f'(f(x))*f'(x) = g(f(x))*g(x)



-- 
FE

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