Differential Equation Involving Natural Log.

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SUMMARY

The discussion focuses on evaluating the definite integral \(\int^{-4}_{-6} (x^{-1}+5x)dx\). The user simplifies the integral to \(\ln(-4) - \ln(-6) + 10\), but encounters an issue with the natural logarithm of negative numbers, which is undefined. The correct approach involves recognizing the need for absolute values in the antiderivative \(\int \frac{1}{x}\,dx = \ln |x| + C\), particularly when dealing with negative limits.

PREREQUISITES
  • Understanding of definite integrals
  • Familiarity with natural logarithms and their properties
  • Knowledge of antiderivatives and integration techniques
  • Basic calculus concepts, including limits and continuity
NEXT STEPS
  • Study the properties of natural logarithms, particularly with negative arguments
  • Learn about improper integrals and how to handle undefined expressions
  • Explore the concept of absolute values in integration
  • Practice additional examples of definite integrals involving logarithmic functions
USEFUL FOR

Students studying calculus, particularly those tackling integration techniques and the properties of logarithmic functions. This discussion is beneficial for anyone seeking to understand the nuances of evaluating integrals with negative limits.

theRukus
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Homework Statement


Calculate the following:
[itex]\int^{-4}_{-6} (x^-1+5x)dx[/itex]


Homework Equations





The Attempt at a Solution


I've worked this down to
[itex]ln(-4) + 5(-4) - ln(-6) - 5(-6)<br /> =ln(-4)-ln(-6)+10[/itex]
The answer to the left half (the ln parts) of the equation is undefined, and the right is 10..
So... undefined + 10? I'm unsure what to say the definite answer is...

Thank you for any help.
 
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The antiderivative is

[tex]\int \frac 1 x\,dx = \ln |x|+C[/tex]

The absolute value signs matter when x < 0.
 

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