Limit Considerations w/o L'Hôpital on a Quotient of Root Expressions

  • Thread starter Thread starter tellmesomething
  • Start date Start date
  • Tags Tags
    Limits
Click For Summary
SUMMARY

The discussion focuses on evaluating the limit $$\lim_{x\to 1} \frac{\sqrt[n]{x}-1}{\sqrt[m]{x}-1}$$ without using L'Hôpital's Rule, which is applicable due to the 0/0 indeterminate form. The suggested approach involves rationalizing the expressions and utilizing the identity $$t^n - 1 = (t-1)(t^{n-1} + t^{n-2} + \cdots + t + 1)$$ with $$t = \sqrt[n]{x}$$ to simplify the limit. This method allows for the computation of the limit by breaking it down into manageable parts, specifically $$\lim_{x\to 1} \frac{\sqrt[n]{x}-1}{x-1}$$ and $$\lim_{x\to 1} \frac{x-1}{\sqrt[m]{x}-1}$$.

PREREQUISITES
  • Understanding of limits and indeterminate forms in calculus.
  • Familiarity with the properties of roots and exponents.
  • Knowledge of algebraic identities, specifically the factorization of polynomials.
  • Basic skills in manipulating expressions involving square roots and higher roots.
NEXT STEPS
  • Study the application of the limit definition in calculus.
  • Learn about rationalizing techniques for limits involving roots.
  • Explore the use of polynomial identities in limit evaluations.
  • Investigate alternative methods for resolving indeterminate forms, such as Taylor series expansion.
USEFUL FOR

Students and educators in calculus, mathematicians focusing on limit evaluations, and anyone seeking to deepen their understanding of non-L'Hôpital methods for solving limits involving root expressions.

tellmesomething
Messages
449
Reaction score
59
Homework Statement
$$\lim_{x\to 1} \frac{\sqrt[n]{x}-1}{\sqrt[m]{x}-1}$$ (##m## and ##n## are integers)
Relevant Equations
None
I know how to do this using lopital since its a 0/0 indeterminate form. However I would like to do it without using lopital as well..how should I go about it? For starters I thought of rationalizing the numerator and denominator but we cant necessarily apply the (a+b)(a-b) identity since we dont know if m and n are odd or even integers.. Please provide a hint..
 
Physics news on Phys.org
Observe $$\lim_{x\to 1} \frac{\sqrt[n]{x}-1}{\sqrt[m]{x}-1} = \lim_{x\to 1} \frac{\sqrt[n]{x} -1}{x-1} \cdot \lim_{x\to 1} \frac{x-1}{\sqrt[m]{x}-1}$$ Use the identity $$t^n - 1 = (t-1)(t^{n-1} + t^{n-2} + \cdots + t + 1)$$ with ##t = \sqrt[n]{x}## to simplify ##\lim_{x\to 1} \frac{\sqrt[n]{x}-1}{x-1}##. Use a similar factorization to compute ##\lim_{x\to 1} \frac{x-1}{\sqrt[m]{x}-1}##.
 
  • Like
Likes   Reactions: PeroK, FactChecker and tellmesomething
Euge said:
$$t^n - 1 = (t-1)(t^{n-1} + t^{n-2} + \cdots + t + 1)$$
Thankyou! I was looking for this general form.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 21 ·
Replies
21
Views
3K
  • · Replies 3 ·
Replies
3
Views
7K
  • · Replies 8 ·
Replies
8
Views
3K
Replies
8
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 25 ·
Replies
25
Views
1K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 4 ·
Replies
4
Views
3K
  • · Replies 5 ·
Replies
5
Views
4K