Solving a very strange improper integral

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SUMMARY

The improper integral under discussion is defined as \int_0^{\infty}\frac{cos(x)+sin(x)}{1+v^2}dv = \pi \cdot e^{-x}. The solution involves separating the integral into two parts: \int_0^{1}\frac{cos(x)}{1+v^2}dv and \int_1^{\infty}\frac{sin(x)}{1+v^2}dv. The integral \int\frac{dv}{1+ v^2}= arctan(v)+ C is noted, but it does not yield the expected result of \pi e^{-x}. The discussion suggests a potential error in the problem statement regarding the relationship between x and v.

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Susanne217
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Homework Statement



I am getting fooled by the this improper integral


\int_0^{\infty}\frac{cos(x)+sin(x)}{1+v^2}dv = \pi \cdot e^{-x}

How the devil do I go about getting that result?


The Attempt at a Solution



I end up getting the sum of the two integrals

\int_0^{1}\frac{cos(x)}{1+v^2}dv + \int_1^{\infty}\frac{sin(x)}{1+v^2}dv but how do I proceed from there? Hints please :)
 
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is x a constant term here?
 
Since you are integrating with respect to v, this is just
(cos(x)+ sin(x))\int_0^\infty \frac{dv}{1+ v^2}


And you should know that
\int\frac{dv}{1+ v^2}= arctan(v)+ C.

But that is NOT equal to \pi e^{-x}. You must have copied the problem incorrectly or left out some relationship between x and v.
 

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