Limit involving natural log

In summary, the limit of (tanx)^cosx as x-->infinity cannot be solved using L'Hopital's rule and is not a valid indeterminate form. The limit does not exist.
  • #1
fk378
367
0

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
 
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  • #2
"the limit of cosx as x-->infinity is 1 (or is it infinity?)"
That limit doesn't exist.
 
  • #3
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
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
I just noticed in the directions it says to rearrange the problem so that you can use L'Hopital's rule.
 
  • #6
fk378 said:
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
 

What is the definition of a limit involving natural log?

A limit involving natural log is a mathematical concept that describes the behavior of a function as its input approaches a specific value. It is denoted as lim x→a f(x), where f(x) is a function and a is the value the input is approaching.

What is the significance of natural log in limits?

Natural log, or ln(x), is the inverse of the exponential function e^x. It is commonly used in limits because it has a special property that allows for easier evaluation of certain limits.

How do you evaluate a limit involving natural log?

To evaluate a limit involving natural log, you can use algebraic manipulation, L'Hopital's rule, or the properties of limits. It is important to consider the domain of the function and any restrictions on the variable in order to properly evaluate the limit.

What are some common types of limits involving natural log?

Some common types of limits involving natural log include limits at infinity, limits of quotients, and limits of composite functions. These types of limits often require different techniques for evaluation.

Can a limit involving natural log have a non-numeric value?

Yes, a limit involving natural log can have a non-numeric value, such as infinity or undefined. This can occur if the function has a vertical asymptote or if the limit does not exist due to oscillation or divergence.

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