Solving an Indeterminate Limit with L'Hospital's Rule

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In summary, L'Hospital's Rule is a mathematical technique used to evaluate limits that result in indeterminate forms. It should be applied when evaluating limits that involve trigonometric, exponential, or logarithmic functions. To use it, the limit needs to be rewritten as a quotient of two functions and the derivative of each function is taken separately. There are limitations to using this rule, such as only being applicable to certain types of functions and the need to check certain conditions. Alternative techniques for solving indeterminate limits include algebraic manipulation, substitution, and series expansions. However, L'Hospital's Rule is a useful and efficient method for solving many types of indeterminate limits.
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student85
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Homework Statement


find the limit:

lim (lnx)^3 / x
x-->(infinity)


Homework Equations


It's a L´hospital homework so that should be what I need to use.


The Attempt at a Solution


However, when using L'Hospital, I get nowhere since I keep getting indeterminations.
Help is appreciated.
 
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  • #2
You'll have to repeatedly use L'Hopital until you get to a non-indeterminant. Takes 4 times, I think.
 
  • #3
damn, it gets pretty nasty...
Thanks.
 
  • #4
Nasty how? It's just a little repetitious.
 

Related to Solving an Indeterminate Limit with L'Hospital's Rule

1. What is L'Hospital's Rule for solving indeterminate limits?

L'Hospital's Rule is a mathematical technique used to evaluate limits of functions that result in an indeterminate form, such as 0/0 or ∞/∞. It states that for a given function f(x) and g(x), if the limit of f(x)/g(x) exists and is equal to an indeterminate form, then the limit of f(x)/g(x) is equal to the limit of the derivatives of f(x) and g(x).

2. When should L'Hospital's Rule be applied?

L'Hospital's Rule should be applied when evaluating limits that result in indeterminate forms, such as 0/0, ∞/∞, or 0*∞. It is also useful for evaluating limits of functions that involve trigonometric, exponential, or logarithmic functions.

3. How do you use L'Hospital's Rule to solve an indeterminate limit?

To use L'Hospital's Rule, you first need to rewrite the limit as a quotient of two functions. Then, take the derivative of the numerator and denominator separately. If the resulting limit still results in an indeterminate form, you can repeat the process until the limit can be evaluated. If the limit does not result in an indeterminate form, then the limit is equal to the resulting value.

4. Are there any limitations to using L'Hospital's Rule?

Yes, there are some limitations to using L'Hospital's Rule. It can only be applied to limits that result in indeterminate forms, and it may not work for all types of functions. Additionally, it is important to check the conditions for the rule to be applicable, such as ensuring that the limit of the quotient of the derivatives exists.

5. Are there any alternatives to using L'Hospital's Rule for solving indeterminate limits?

Yes, there are alternative techniques for solving indeterminate limits, such as algebraic manipulation, substitution, or using series expansions. However, L'Hospital's Rule is a useful and efficient method for solving many types of indeterminate limits, especially those involving trigonometric, exponential, or logarithmic functions.

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