Evaluate Limit: $$\lim_{x\to\infty} (-1)^nn^3 + 2^{-n}$$

  • Context: MHB 
  • Thread starter Thread starter tmt1
  • Start date Start date
  • Tags Tags
    Limit
Click For Summary
SUMMARY

The limit $$\lim_{n\to\infty} (-1)^n n^3 + 2^{-n}$$ does not exist due to the divergent nature of the alternating sequence of cubes, which oscillates between positive and negative values. While the term $$2^{-n}$$ approaches zero as $$n$$ approaches infinity, the dominant term $$(-1)^n n^3$$ diverges. Therefore, L'Hopital's rule is not applicable in this scenario, confirming that the limit is undefined.

PREREQUISITES
  • Understanding of limits in calculus
  • Familiarity with alternating sequences
  • Knowledge of L'Hopital's rule and its applications
  • Basic concepts of convergence and divergence in sequences
NEXT STEPS
  • Study the properties of alternating sequences in calculus
  • Learn about the application and limitations of L'Hopital's rule
  • Explore the concept of divergence in sequences and series
  • Investigate other methods for evaluating limits involving oscillating functions
USEFUL FOR

Students of calculus, mathematicians analyzing limits, and educators teaching concepts of convergence and divergence in sequences.

tmt1
Messages
230
Reaction score
0
I have this limit:

$$\lim_{{x}\to{\infty}} {(-1)}^{n}{n}^{3} + {2}^{-n}$$

and I'm unsure how to evaluate it or how to apply L'hopital's rule to this limit.
 
Physics news on Phys.org
tmt said:
I have this limit: $$\lim_{n\to\infty} (-1)^n\,n^3 + 2^{-n}$$

and I'm unsure how to evaluate it or how to apply L'hopital's rule to this limit.
L'Hopital's rule doesn't apply here.

We see that: \lim_{n\to\infty}2^{-n}\:=\:0

But the first part is an alternating sequence of cubes:
. . -1 + 8 - 27 + 64 - 125 + \cdots which diverges.

 
It's a limit, not a series - the limit does not exist.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K