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Write the terms \(a_{1}, a_{2}, a_{3},\) and \(a_{4}\) of the following sequences. If the sequence appears to converge, make a conjecture about its limit. If the sequence diverges, explain why. $$a_{n+1}=1-\frac{a_{n}}{2} ; a_{0}=\frac{2}{3}$$

Short Answer

Expert verified
Question: Find the convergence and conjecture the limit for the sequence defined by \(a_0 = \frac{2}{3}\) and \(a_{n+1}=1-\frac{a_{n}}{2}\). Answer: The sequence converges and its limit is \(\frac{2}{3}\).

Step by step solution

01

Identify the first term of the sequence and formula for the next term

The exercise gives us the initial term \(a_0 = \frac{2}{3}\) and the formula for the next term in the sequence: \(a_{n+1}=1-\frac{a_{n}}{2}\).
02

Calculate the first four terms of the sequence

Using the given formula, we can calculate the first four terms of the sequence: 1. \(a_1 = 1 - \frac{a_0}{2} = 1 - \frac{\frac{2}{3}}{2}= 1 - \frac{1}{3} = \frac{2}{3}\) 2. \(a_2 = 1 - \frac{a_1}{2} = 1 - \frac{\frac{2}{3}}{2} = 1 - \frac{1}{3} = \frac{2}{3}\) 3. \(a_3 = 1 - \frac{a_2}{2} = 1 - \frac{\frac{2}{3}}{2} = 1 - \frac{1}{3} = \frac{2}{3}\) We can see that terms of the sequence are not changing: \(a_0 = a_1 = a_2 = a_3\). Moreover, the formula \(a_{n+1}=1-\frac{a_{n}}{2}\) is always the same. Therefore, the sequence will continue to be the same for any \(a_n\).
03

Determine if the sequence converges or diverges

We can see that the terms of the sequence are not changing; they are always constant and equal to \(\frac{2}{3}\). Hence, the sequence converges.
04

State the conjecture about the limit of the sequence

Since the terms of the sequence are always constant and equal to \(\frac{2}{3}\), we can conjecture that the sequence converges to the limit \(\lim_{n\to \infty} a_n = \frac{2}{3}\).

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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 limit of a sequence represents the value that the terms of a sequence get closer to as the number of terms increases indefinitely. In simpler terms, as you progress through the sequence, the terms settle towards a specific number. Understanding this concept is fundamental in mathematics, especially when analyzing patterns or trends within a sequence.

To find the limit of a sequence, we often observe the behavior of the sequence as it progresses. For example, in the provided exercise, all terms are equal to \( \frac{2}{3} \), regardless of how far you continue in the sequence. This consistent term value is a strong indicator that the sequence is approaching, or converging to, the limit \( \frac{2}{3} \).

Recognizing the limit helps us understand whether a sequence eventually becomes stable or not. In the context of this exercise, the understanding of the limit allows us to conclude that any \( a_n \) will equal \( \frac{2}{3} \) as \( n \) becomes very large. It is a key feature that helps define the nature of the sequence, whether it converges or is still moving towards a particular value.
Recursive Sequences
Recursive sequences are sequences in which each term after the first is defined as a function of the preceding term(s). Virtually, you're using the previous term to calculate the next. This kind of sequence is vital in mathematics because it enables the creation of very complex sequences from simple rules.

Let's look at the current exercise: the recursive rule given is \( a_{n+1} = 1-\frac{a_n}{2} \), starting with \( a_0 = \frac{2}{3} \). The sequence is naturally recursive since each term is derived by applying the formula to the previous term. This pattern ensures that we do not need a separate formula for each term but instead apply the same rule iteratively.

Recursive sequences can be simple or complex, but understanding the rule helps solve the sequence systematically. One significant outcome of such sequences is affected by the initial term, which can greatly influence the entire sequence's behavior. In the given example, the sequence doesn't change because the rule and initial condition are perfectly balanced to keep the terms constant.
Convergent Series
A convergent series is a series of numbers whose terms approach a specific limit as more terms are added. When discussing convergence in the series, we're examining whether partial sums (sums of the first \( n \) terms) settle around a particular number. This concept extends the idea of sequence convergence into sums of infinite terms.

In the context of our exercise, although not explicitly a series problem, the sequence itself is related by how it approaches convergence. If the sequence were to be seen as terms added together (such as summing constant values), it would imply that the series formed is also converging, likely toward infinity if adding infinite times a constant like \( \frac{2}{3} \).

Understanding convergent series is crucial in mathematical analysis because it deals with the sum's behavior as the number of terms reaches infinity. It allows mathematicians to deal with infinite processes under a finite framework, which is powerful in calculus and mathematical predictions. In our example case, the sequence demonstrates stability and convergence before we even enter the domain of series and sums.

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Most popular questions from this chapter

The expression $$1+\frac{1}{1+\frac{1}{1+\frac{1}{1+\frac{1}{1+}}}}.$$ where the process continues indefinitely, is called a continued fraction. a. Show that this expression can be built in steps using the recurrence relation \(a_{0}=1, a_{n+1}=1+1 / a_{n},\) for \(n=0,1,2,3, \ldots . .\) Explain why the value of the expression can be interpreted as \(\lim _{n \rightarrow \infty} a_{n},\) provided the limit exists. b. Evaluate the first five terms of the sequence \(\left\\{a_{n}\right\\}\). c. Using computation and/or graphing, estimate the limit of the sequence. d. Assuming the limit exists, use the method of Example 5 to determine the limit exactly. Compare your estimate with \((1+\sqrt{5}) / 2,\) a number known as the golden mean. e. Assuming the limit exists, use the same ideas to determine the value of $$a+\frac{b}{a+\frac{b}{a+\frac{b}{a+\frac{b}{a+}}}}$$ where \(a\) and \(b\) are positive real numbers.

A ball is thrown upward to a height of \(h_{0}\) meters. After each bounce, the ball rebounds to a fraction r of its previous height. Let \(h_{n}\) be the height after the nth bounce and let \(S_{n}\) be the total distance the ball has traveled at the moment of the nth bounce. a. Find the first four terms of the sequence \(\left\\{S_{n}\right\\}\) b. Make a table of 20 terms of the sequence \(\left\\{S_{n}\right\\}\) and determine \(a\) plausible value for the limit of \(\left\\{S_{n}\right\\}\) $$h_{0}=20, r=0.5$$

$$\text {Evaluate each series or state that it diverges.}$$ $$\sum_{k=1}^{\infty} \frac{(-2)^{k}}{3^{k+1}}$$

Consider the following situations that generate a sequence. a. Write out the first five terms of the sequence. b. Find an explicit formula for the terms of the sequence. c. Find a recurrence relation that generates the sequence. d. Using a calculator or a graphing utility, estimate the limit of the sequence or state that it does not exist. Jack took a \(200-\mathrm{mg}\) dose of a painkiller at midnight. Every hour, \(5 \%\) of the drug is washed out of his bloodstream. Let \(d_{n}\) be the amount of drug in Jack's blood \(n\) hours after the drug was taken, where \(d_{0}=200 \mathrm{mg}\)

For a positive real number \(p,\) the tower of exponents \(p^{p^{p}}\) continues indefinitely and the expression is ambiguous. The tower could be built from the top as the limit of the sequence \(\left\\{p^{p},\left(p^{p}\right)^{p},\left(\left(p^{p}\right)^{p}\right)^{p}, \ldots .\right\\},\) in which case the sequence is defined recursively as \(a_{n+1}=a_{n}^{p}(\text { building from the top })\) where \(a_{1}=p^{p} .\) The tower could also be built from the bottom as the limit of the sequence \(\left\\{p^{p}, p^{\left(p^{p}\right)}, p^{\left(p^{(i)}\right)}, \ldots .\right\\},\) in which case the sequence is defined recursively as \(a_{n+1}=p^{a_{n}}(\text { building from the bottom })\) where again \(a_{1}=p^{p}\). a. Estimate the value of the tower with \(p=0.5\) by building from the top. That is, use tables to estimate the limit of the sequence defined recursively by (1) with \(p=0.5 .\) Estimate the maximum value of \(p > 0\) for which the sequence has a limit. b. Estimate the value of the tower with \(p=1.2\) by building from the bottom. That is, use tables to estimate the limit of the sequence defined recursively by (2) with \(p=1.2 .\) Estimate the maximum value of \(p > 1\) for which the sequence has a limit.

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