Chapter 9: Problem 117
Which of the sequences converge, and which diverge? Give reasons for your answers. $$a_{n}=\frac{2^{n}-1}{2^{n}}$$
Short Answer
Expert verified
The sequence converges to 1.
Step by step solution
01
Understand the Sequence
We have the sequence \(a_n = \frac{2^n - 1}{2^n}\). Our task is to determine whether this sequence converges or diverges.
02
Express the Sequence in a Simplified Form
We can simplify the expression for better analysis: \[ a_n = \frac{2^n - 1}{2^n} = \frac{2^n}{2^n} - \frac{1}{2^n} = 1 - \frac{1}{2^n}. \] This expression helps us see the behavior of the sequence more clearly.
03
Analyze the Limit of the Sequence
Let's find the limit of \(a_n\) as \(n\) approaches infinity: \(\lim_{{n\to\infty}} a_n = \lim_{{n\to\infty}} \left(1 - \frac{1}{2^n}\right)\). As \(n\) becomes very large, \(\frac{1}{2^n}\) approaches 0.
04
Find the Exact Limit
With \(\frac{1}{2^n}\) approaching 0 as \(n\to\infty\), the expression \(1 - \frac{1}{2^n}\) approaches \(1 - 0 = 1\). Therefore, \(\lim_{{n\to\infty}} a_n = 1\).
05
Conclusion About Convergence
Since the limit of \(a_n\) as \(n\to\infty\) is 1, the sequence \(a_n = \frac{2^n - 1}{2^n}\) converges to 1.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Limit of a Sequence
The concept of the limit of a sequence is crucial when analyzing whether sequences converge or diverge. A sequence is essentially a list of numbers written in a specific order. When we discuss the limit, we are trying to determine what value the terms of the sequence approach as the sequence progresses towards infinity.
If the sequence approaches a particular numeric value, it is said that the sequence converges to that value. Mathematically, a sequence \(a_n\) has a limit \(L\) if for every small number \(\epsilon > 0\), there is a number \(N\) such that for all \(n > N\), the terms \(a_n\) are within \(\epsilon\) units of \(L\). In simpler terms, the sequence gets closer and closer to the limit \(L\) as \(n\) becomes very large. In our exercise, the sequence \(a_n = \frac{2^n - 1}{2^n}\) has a limit of 1 as \(n\) approaches infinity.
If the sequence approaches a particular numeric value, it is said that the sequence converges to that value. Mathematically, a sequence \(a_n\) has a limit \(L\) if for every small number \(\epsilon > 0\), there is a number \(N\) such that for all \(n > N\), the terms \(a_n\) are within \(\epsilon\) units of \(L\). In simpler terms, the sequence gets closer and closer to the limit \(L\) as \(n\) becomes very large. In our exercise, the sequence \(a_n = \frac{2^n - 1}{2^n}\) has a limit of 1 as \(n\) approaches infinity.
Simplifying Expressions
Simplifying expressions is an important step to make sequence analysis easier. In the given sequence \(a_n = \frac{2^n - 1}{2^n}\), we simplify it to \( a_n = 1 - \frac{1}{2^n} \).
This simplification helps to clearly observe the behavior of the sequence:
This simplification helps to clearly observe the behavior of the sequence:
- The first term \(1\) is constant and direct.
- The second term \(\frac{1}{2^n}\) becomes very small as \(n\) increases.
Infinite Limit
Not all sequences have a finite limit; some may approach infinity. However, in the context of infinite limits, we often look to see if parts of the sequence tend toward zero to determine convergence to a finite value.
In our simplified sequence \(a_n = 1 - \frac{1}{2^n}\), as \(n\) becomes large, \(\frac{1}{2^n}\) shrinks towards zero. This behavior indicates that adding or subtracting a vanishingly small number makes the sequence approach 1, a finite limit.
This demonstrates that the sequence does not approach infinity but rather a fixed numeric value, affirming its convergence.
In our simplified sequence \(a_n = 1 - \frac{1}{2^n}\), as \(n\) becomes large, \(\frac{1}{2^n}\) shrinks towards zero. This behavior indicates that adding or subtracting a vanishingly small number makes the sequence approach 1, a finite limit.
This demonstrates that the sequence does not approach infinity but rather a fixed numeric value, affirming its convergence.
Convergent Sequences
Convergent sequences are those that tend to a specific limit as the number of terms grows infinitely. Recognizing a sequence as convergent helps us understand that eventually, the sequence stabilizes around a particular value.
For the sequence \(a_n = \frac{2^n - 1}{2^n}\), we've shown simplification to \(1 - \frac{1}{2^n}\) leads us to confirm the sequence converges to 1.
For the sequence \(a_n = \frac{2^n - 1}{2^n}\), we've shown simplification to \(1 - \frac{1}{2^n}\) leads us to confirm the sequence converges to 1.
- As \(n\) increases, \(\frac{1}{2^n}\) decreases.
- Thus, \(a_n\) increasingly approximates 1.