Integral involving the derivative

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    Derivative Integral
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SUMMARY

The integral of the form \(\int \frac{f'(x)}{f^{2}(x)}dx\) can be simplified using the substitution \(u = f(x)\), leading to \(\int u^{-2}\,du\). This transformation utilizes the relationship \(du = f'(x)dx\), allowing for the application of the power rule. The discussion confirms that both direct rewriting and substitution yield the same result, demonstrating the flexibility of integration techniques in calculus.

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Yankel
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Hello,

I am trying to calculate the following integral:

\[\int \frac{f'(x)}{f^{2}(x)}dx\]

I suspect is has something to do with the rule of f'(x)/f(x), with the ln, but there must be more to it than that.

can you assist please ? Thank you !
 
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I would rewrite the given integral as:

$$\int f^{-2}\,df$$

Now just use the power rule. :)
 
Can you explain your solution please ? How did you go from the derivative and dx to f only with df ?
 
$$\int \frac{f'(x)}{f^2(x)}\,dx=\int f^{-2}\d{f}{x}\,dx=\int f^{-2}\,df$$
 
Right. Simple...

Could you get the same result from the substitution rule ?
 
Yankel said:
Right. Simple...

Could you get the same result from the substitution rule ?

Yes, I suppose we could write:

$$u=f(x)\implies du=f'(x)\,dx$$

And now we have:

$$\int u^{-2}\,du$$

That seems a little roundabout to me, but perfectly legitimate. :D
 

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