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Limit involving natural log

  • Thread starter fk378
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  • #1
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Homework Statement


Find the limit of (tanx)^cosx as x-->infinity
Rearrange the equation so that you can use L'Hopital's rule for the form of (infinity/infinity)



The Attempt at a Solution


I did ln(tanx)^cosx = cosxlntanx
I know the limit of tanx as x-->infinity is pi/2
the limit of cosx as x-->infinity is infinity

Now, I don't know where to go from here
 
Last edited:

Answers and Replies

  • #2
nicksauce
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"the limit of cosx as x-->infinity is 1 (or is it infinity?)"
That limit doesn't exist.
 
  • #3
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Oh okay. So now I have infinity x infinity. I can use L'Hopital's rule but I don't know how to set up the function.
 
  • #4
HallsofIvy
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No, you cannot use L'Hopital's rule for that. "Infinity* infinity" is not one of cases for which you can use L'Hopital's rule- nor do you need to. You have already been told the answer.
 
  • #5
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I just noticed in the directions it says to rearrange the problem so that you can use L'Hopital's rule.
 
  • #6
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I just noticed in the directions it says to rearrange the problem so that you can use L'Hopital's rule.
Well then, what are the special cases in which L'Hopital's Rule can be applied? That is what are indeterminate forms?

Casey
 

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