Integral Problem: Solutions Say Divergent, Help Please!

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SUMMARY

The integral problem discussed involves the function f(x) = 1/|x|, which the user incorrectly integrated, leading to a result of -ln2. However, the correct integral is ∫ 1/|x| dx = sgn(x) ln |x|. The primary error was integrating across a singularity, which resulted in a negative value despite the integrand being positive over the interval from -2 to 1. This indicates a fundamental misunderstanding of the behavior of the integral near singularities.

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Homework Statement



yc8m.jpg



Homework Equations





The Attempt at a Solution



Ive solved it this way:
yc8m.jpg
= [ln |x|]1-2 = ln 1 - ln 2 = -ln2

However the solutions say the integral is divergent, therefore it should tend to +∞ or -∞

If someone could tell me what I've done wrong I'd appreciate!
Thanks
 
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You did two things wrong.

1. Lesser problem: Your integral is incorrect. [itex]\int 1/|x|\,dx = \mathop{\mathrm{sgn}} x \, \ln |x|[/itex], not [itex]\ln |x|[/itex].

2. Huge problem: You integrated across a singularity.f(x)=1/|x| is positive everywhere. How could the integral of this function from -2 to 1 possibly be negative? That you obtained a negative result when the integrand is always positive and the integration interval is in the positive direction should have been a big warning sign indicating that you did something wrong.
 

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