Evaluating improper intergral with trig function

  • Thread starter SteliosVas
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  • #1
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Homework Statement



Okay so the problem is asking simply for a proof for convergence /divergence of the following indefinite integral:

∫(x*sin2(x))/(x3-1) over [2,∞)

Homework Equations



I know I can use substitution method

The Attempt at a Solution



Okay so I know if i factorize the bottom part of the integral I get:

∫(x*sin2(x))/(x-1)(x-1)(x2+x+1).

Now obviously I am not sure if this a very elemetary problem or indeed quite challenging. I have tried substituion making u = (x3-1) but than didn't really work... Not sure what else I should try
 

Answers and Replies

  • #2
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I dont think that the problem wants you to solve the improper integral. Rather, it wants you to perform some test for convergence / divergence.
 
  • #3
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I dont think that the problem wants you to solve the improper integral. Rather, it wants you to perform some test for convergence / divergence.


That's what I thought, as the computation of the improper integral would probably be too challenging... Should I use the limit test? In other words compare the overall function to the convergence/divergence of 1/x3 as it approaches 2
 
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  • #4
Ray Vickson
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That's what I thought, as the computation of the improper integral would probably be too challenging... Should I use the limit test? In other words compare the overall function to the convergence/divergence of 1/x3 as it approaches 2

You don't need to worry about the lower limit x = 2, because nothing bad happens to the integrand ##f(x) = x \sin^2(x)/(x^3-1)## as ##x \to 2##. However, you do need to worry about the upper limit as ##x \to \infty##. Your textbook and/or course notes must have some relevant tests to use; try out some of them, then come back here if you still have some questions and issues.
 

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