Simple Indefinite Integral of \int\frac{4}{-e^{4x-7}} = ln(-e^{4x-7}) = -4x+7+C

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Homework Help Overview

The discussion revolves around the evaluation of a simple indefinite integral involving an exponential function. Participants are examining the integration of the expression \(\int\frac{4}{-e^{4x-7}}\,dx\) and comparing their results with a provided answer.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the application of the natural logarithm in the integration process, particularly regarding the assumption that \(\ln{e}=1\) applies uniformly to all forms of integrals involving logarithmic expressions. Some are exploring where their reasoning may have diverged from the correct approach.

Discussion Status

There is an ongoing exploration of the reasoning behind the integration steps, with some participants affirming the correctness of the book's answer. The discussion includes attempts to identify specific errors in the original poster's reasoning, particularly related to the properties of logarithms.

Contextual Notes

Participants are navigating the complexities of integrating functions involving logarithmic and exponential forms, with an emphasis on understanding the assumptions that underlie these mathematical operations.

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\int\frac{4}{-e^{4x-7}}

=ln-e^{4x-7}}

=-4x+7+C

The answer says it is:

=\-e^{-4x+7}+C
 
Last edited:
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The book is right, which is easily verifiable by computing the derivative the given answer.
 
D H said:
The book is right.

Is there somewhere I went wrong? I am guessing it has something to do with the ln.
I thought that

\ln{e}=1

Therefore: ln-e^{4x-7}}=-4x+7+C
 
Last edited:
Yes, the problem is with the natural logarithm.

Just because \int \frac 1 x \,dx = \ln x does not mean that everything of the form \int \frac 1{f(x)}\,dx integrates to \ln(f(x)).
 

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