Proving Sequence Convergence: ||s_n|-|L|| < epsilon

In summary, for any a, b in R, the absolute value of the difference between the absolute values of a and b is less than or equal to the absolute value of the difference between a and b. To prove that the absolute value of a sequence {s_n} converges to the absolute value of L, we can use the Squeeze Theorem or substitute in epsilon values to show the convergence.
  • #1
tarheelborn
123
0

Homework Statement


For any a, b in R, show that ||a|-|b|| <= |a-b|. Then prove that {|s_n|} converges to |L| if {s_n} converges to L.

Homework Equations





The Attempt at a Solution


For the first part, ||a|-|b|| = |a-b| by the triangle inequality. For the second part, ||s_n|-0| < epsilon implies that |s_n -0| < epsilon, but I am not sure how to work that around to the L's.
 
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  • #2
tarheelborn said:
For the first part, ||a|-|b|| = |a-b| by the triangle inequality.

What? For example:
[itex]\big|\,|2|-|-2|\,\big| = |2-(-2)|[/itex]
?
 
  • #3
Get the [tex]| |a| - |b| | \leq |a - b|[/tex] right first. The second part just follows by the Squeeze Theorem, or more simply, just "shove in the epsilons" if you know what I mean.
 

1. What is the purpose of proving sequence convergence?

The purpose of proving sequence convergence is to determine whether or not a given sequence of numbers approaches a specific value, known as the limit, as the sequence progresses to infinity. This is important in many fields of science and mathematics, as it allows for the prediction of future values and behavior of systems.

2. How is sequence convergence typically proven?

Sequence convergence is typically proven by using mathematical techniques such as the limit definition, the ratio test, or the root test. These methods involve analyzing the behavior of the sequence as it approaches infinity and comparing it to a known limit value.

3. What does the notation ||s_n|-|L|| < epsilon mean?

The notation ||s_n|-|L|| < epsilon represents the definition of sequence convergence, stating that for a given sequence s_n and limit value L, the difference between the absolute value of s_n and the absolute value of L must be less than a small positive value epsilon. This ensures that as n approaches infinity, the terms of the sequence get closer and closer to the limit value.

4. What is the significance of the value epsilon in proving sequence convergence?

The value epsilon is significant because it determines the accuracy and precision of the convergence of the sequence. A smaller value of epsilon indicates a higher level of precision, as the terms of the sequence must be closer to the limit value in order for the condition to be met.

5. Can a sequence converge to more than one limit value?

No, a sequence can only converge to one limit value. If a sequence converges to more than one limit value, it is said to be divergent and does not have a well-defined limit.

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