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Write the first five terms of the sequence \(\left\\{a_{n}\right\\}\), \(n=0,1,2,3, \ldots\), and find \(\lim _{n \rightarrow \infty} a_{n^{*}}\) $$ a_{n}=\frac{n^{2}+5}{n^{2}+1} $$

Short Answer

Expert verified
The first five terms are 5, 3, 1.8, 1.4, and 1.235; the limit is 1.

Step by step solution

01

Write the Expression for the Sequence

First, we need to understand the given expression for the sequence. The sequence is defined as \( a_{n} = \frac{n^{2}+5}{n^{2}+1} \). We will use this expression to find the terms of the sequence.
02

Calculate the First Term

For the first term, set \( n = 0 \): \[a_{0} = \frac{0^{2} + 5}{0^{2} + 1} = \frac{5}{1} = 5. \]The first term, \( a_0 \), is 5.
03

Calculate the Second Term

For the second term, set \( n = 1 \): \[a_{1} = \frac{1^{2} + 5}{1^{2} + 1} = \frac{6}{2} = 3.\]The second term, \( a_1 \), is 3.
04

Calculate the Third Term

For the third term, set \( n = 2 \): \[a_{2} = \frac{2^{2} + 5}{2^{2} + 1} = \frac{9}{5} = 1.8.\]The third term, \( a_2 \), is 1.8.
05

Calculate the Fourth Term

For the fourth term, set \( n = 3 \): \[a_{3} = \frac{3^{2} + 5}{3^{2} + 1} = \frac{14}{10} = 1.4.\]The fourth term, \( a_3 \), is 1.4.
06

Calculate the Fifth Term

For the fifth term, set \( n = 4 \): \[a_{4} = \frac{4^{2} + 5}{4^{2} + 1} = \frac{21}{17} \approx 1.235.\]The fifth term, \( a_4 \), is approximately 1.235.
07

Find the Limit as \\( n \\rightarrow \\infty \\)

The limit of the sequence as \( n \to \infty \) is given by: \[\lim _{n \rightarrow \infty} a_{n} = \lim _{n \rightarrow \infty} \frac{n^{2}+5}{n^{2}+1} = \lim _{n \rightarrow \infty} \frac{1 + \frac{5}{n^{2}}}{1 + \frac{1}{n^{2}}} = 1.\]This happens because as \( n \) becomes very large, the terms \( \frac{5}{n^{2}} \) and \( \frac{1}{n^{2}} \) approach zero.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Sequence and Series
A sequence is a list of numbers arranged in a specific order. In our example, the sequence is described by the formula \( a_{n} = \frac{n^{2} + 5}{n^{2} + 1} \). Sequences can either converge to a limit or diverge. When sequences have a limit, they approach a specific value as \( n \) grows larger.
A series is the sum of the terms of a sequence. However, in the context of this exercise, we're more interested in observing how individual terms in a sequence unfold. For the given sequence, each term is generated by substituting \( n \) with consecutive natural numbers, i.e., \( n = 0, 1, 2, 3, \ldots \).
When we calculate the first terms, we encounter:
  • \(a_0 = 5\)
  • \(a_1 = 3\)
  • \(a_2 = 1.8\)
  • \(a_3 = 1.4\)
  • \(a_4 \approx 1.235\)
We are noticing how each term substantially decreases as \( n \) increases. This frequent feature of sequences in calculus helps in predicting behavior at large \( n \) values.
Calculus for Biology
Calculus is an invaluable tool in biology, providing methods to model and analyze dynamic systems. Sequences and limits are crucial in understanding processes like population growth, enzyme reactions, and more.
In biology, an understanding of limits helps explain how certain biological systems stabilize over time. This is similar to finding the limit of a sequence in calculus.
For instance, consider a population that grows according to a particular pattern. Initially, growth occurs rapidly but eventually levels off as resources become limited.
  • This leveling off behavior mirrors what we found in the exercise: as \( n \rightarrow \infty \), the sequence approaches its limit of 1.
  • Biologically, this model might predict populations reaching a stable size when growth factors match constraints.
Using calculus, biologists can gain insights into such models and make informed predictions.
Infinite Limits
Infinite limits deal with the behavior of functions as they extend towards infinity, either in their domain or range. In sequences, as \( n \) approaches infinity, we investigate whether terms tend to stabilize at a certain value.
Calculating the limit of the sequence \( a_{n} = \frac{n^{2} + 5}{n^{2} + 1} \) involved comparing dominant terms:
  • The terms \(\frac{5}{n^{2}}\) and \(\frac{1}{n^{2}}\) vanish as \(n\) becomes very large.
  • The higher degree terms \( n^2 \) in numerator and denominator dominate, simplifying our task to looking at \(\frac{1 + \frac{5}{n^{2}}}{1 + \frac{1}{n^{2}}} = 1\) as \(n\) approaches infinity.

Understanding these concepts is key to solving complex calculus problems, especially those involving real-world applications where determining behavior notably "in the long run" is required.

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Most popular questions from this chapter

You do not know whether a drug has zeroth order or first order elimination kinetics. You will use data to determine which type of kinetics it has. You measure the concentration of the drug (in \(\mathrm{mg} / \mathrm{ml}\) ) at time \(t=0\) and at time \(t=1 .\) No drug is added to the blood between \(t=0\) and \(t=1\). You measure the following data: \begin{tabular}{ll} \hline \(\boldsymbol{t}\) & \(\boldsymbol{c}_{t}\) \\ \hline 0 & 40 \\ 1 & 32 \\ \hline \end{tabular} (a) Assume that the drug has zeroth order kinetics. What amount is eliminated from the blood each hour? (b) Assume that the drug has zeroth order kinetics and no more drug is added to the blood. Write a recursion relation for \(c_{t}\) and predict \(c_{2}\). (c) Now assume the drug has first order elimination kinetics. What percentage of drug is eliminated from the blood each hour? (d) Assume that the drug has first order kinetics and no more drug is added. Write a recursion relation for \(c_{t}\) and predict \(c_{2}\). (e) You measure the concentration at time \(t=2\) and find \(c_{2}=\) 25.6. By comparing with your predictions from (b) and (d), decide: Does the drug have zeroth or first order kinetics?

Mountain Gorilla Conservation You are trying to build a mathematical model for the size of the population of mountain gorillas in a national park in Uganda. The data in this question are taken from Robbins et al. (2009). (a) You start by writing a word equation relating the population of gorillas \(t\) years after the study begins, \(N_{t}\), to the population \(N_{t+1}\) in the next year: \(N_{t+1}=N_{t}+\begin{array}{l}\text { number of gorillas } \\ \text { born in one year }\end{array}-\begin{array}{l}\text { number of gorillas } \\\ \text { that die in one yeai }\end{array}\) We will derive together formulas for the number of births and the number of deaths. (i) Around half of gorillas are female, \(75 \%\) of females are of reproductive age, and in a given year \(22 \%\) of the females of reproductive age will give birth. Explain why the number of births is equal to: \(\quad 0.5 \cdot 0.75 \cdot 0.22 \cdot N_{t}=0.0825 \cdot N_{t}\) (ii) In a given year \(4.5 \%\) of gorillas will die. Write down a formula for the number of deaths. (iii) Write down a recurrence equation for the number of gorillas in the national park. Assuming that there are 300 gorillas initially (that is \(N_{0}=300\) ), derive an explicit formula for the number of gorillas after \(t\) years. (iv) Calculate the population size after \(1,2,5\), and 10 years. (v) According to the model, how long will it take for population size to double to 600 gorillas? (b) In reality the population size is almost totally stagnant (i.e., \(N_{t}\) changes very little from year to year). Robbins et al. (2009) consider three different explanations for this effect: (i) Increased mortality: Gorillas are dying sooner than was thought. What percentage of gorillas would have to die each year for the population size to not change from year to year? (ii) Decreased female fecundity: Gorillas are having fewer offspring than was thought. Calculate the female birth rate (percentage of reproductive age females that give birth) that would lead to the population size not changing from year to year. Assume that all other values used in part (a) are correct. (iii) Emigration: Gorillas are leaving the national park. What number of gorillas would have to leave the national park each year for the population to not change from year to year?

Because of complex interactions with other drugs, some drugs have zeroth order elimination kinetics in some circumstances, and first order kinetics in other circumstances, depending on what other drugs are in the patient's system, as well as on age and preexisting medical conditions. Use the data on how concentration varies with time to determine whether the drug has zeroth or first order kinetics. Given the following sequence of measurements for drug concentration, determine whether the drug has zeroth or first order kinetics. $$ \begin{array}{lcccc} \hline \boldsymbol{t} \text { (Hours) } & 0 & 1 & 2 & 3 \\ \hline \boldsymbol{c}_{t} \text { (mg/liter) } & 16 & 12 & 9 & 6.75 \\ \hline \end{array} $$

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