%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % % Scientific Word Wrap/Unwrap Version 2.5 % % Scientific Word Wrap/Unwrap Version 3.0 % % % % If you are separating the files in this message by hand, you will % % need to identify the file type and place it in the appropriate % % directory. The possible types are: Document, DocAssoc, Other, % % Macro, Style, Graphic, PastedPict, and PlotPict. Extract files % % tagged as Document, DocAssoc, or Other into your TeX source file % % directory. Macro files go into your TeX macros directory. Style % % files are used by Scientific Word and do not need to be extracted. % % Graphic, PastedPict, and PlotPict files should be placed in a % % graphics directory. % % % % Graphic files need to be converted from the text format (this is % % done for e-mail compatability) to the original 8-bit binary format. % % % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % % % Files included: % % % % "/document/lec_2_7_00.tex", Document, 44772, 2/9/2000, 10:50:14, "" % % "/document/graphics/maroon0.wmf", ImportPict, 4444, 12/27/1999, 14:32:44, ""% % "/document/graphics/lim1.wmf", ImportPict, 2650, 12/27/1999, 14:57:00, ""% % "/document/graphics/maroon3.wmf", ImportPict, 4444, 12/27/1999, 14:32:44, ""% % "/document/graphics/lim2.wmf", ImportPict, 2974, 12/27/1999, 14:57:00, ""% % "/document/graphics/lim3.wmf", ImportPict, 2974, 12/27/1999, 14:57:02, ""% % "/document/graphics/lim4.wmf", ImportPict, 2934, 12/27/1999, 14:57:02, ""% % "/document/graphics/maroonD.wmf", ImportPict, 4444, 12/27/1999, 14:54:56, ""% % "/document/graphics/maroon6.wmf", ImportPict, 4444, 12/27/1999, 20:52:54, ""% % "/document/graphics/maroon7.wmf", ImportPict, 4444, 12/27/1999, 20:52:54, ""% % % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%% Start /document/lec_2_7_00.tex %%%%%%%%%%%%%%%%%%% %\newtheorem{theorem}{Theorem} %\newtheorem{axiom}[theorem]{Axiom} %\newtheorem{conjecture}[theorem]{Conjecture} %\newtheorem{corollary}[theorem]{Corollary} %\newtheorem{definition}[theorem]{Definition} %\newtheorem{example}[theorem]{Example} %\newtheorem{exercise}[theorem]{Exercise} %\newtheorem{lemma}[theorem]{Lemma} %\newtheorem{proposition}[theorem]{Proposition} %\newtheorem{remark}[theorem]{Remark} \documentclass{article} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \usepackage{graphicx} \usepackage{amsmath} %TCIDATA{OutputFilter=LATEX.DLL} %TCIDATA{Created=Thursday, May 06, 1999 09:11:45} %TCIDATA{LastRevised=Wednesday, February 09, 2000 05:50:12} %TCIDATA{} %TCIDATA{Language=American English} %TCIDATA{CSTFile=webmath.cst} %TCIDATA{PageSetup=72,72,72,72,0} %TCIDATA{AllPages= %F=36,\PARA{038

\hfill \thepage} %} \newtheorem{acknowledgement}[theorem]{Acknowledgement} \newtheorem{algorithm}[theorem]{Algorithm} \newtheorem{case}[theorem]{Case} \newtheorem{claim}[theorem]{Claim} \newtheorem{conclusion}[theorem]{Conclusion} \newtheorem{condition}[theorem]{Condition} \newtheorem{criterion}[theorem]{Criterion} \newtheorem{notation}[theorem]{Notation} \newtheorem{problem}[theorem]{Problem} \newtheorem{solution}[theorem]{Solution} \newtheorem{summary}[theorem]{Summary} \newenvironment{proof}[1][P roof]{\textbf{#1.} }{\ \rule{0.5em}{0.5em}} \input{tcilatex} \begin{document} \section{\protect\vspace{1pt}Ma 116 Lecture 2/7/00} \section{Sequences} \vspace{0in}Please note that in addition to the material below this lecture incorporated material from the Visual Calculus web site. The material on sequences is at \hyperref{Visual Sequences}{}{}{% http://archives.math.utk.edu/visual.calculus/6/}. (To use this link hold down the Ctrl key and click.) \subsection{ Definition} \vspace{0in} \begin{definition} \vspace{1pt}A \emph{sequence} is simply an \emph{ordered list of numbers}, and the numbers in the list are called the \emph{terms} of the sequence. \ There may be a finite or an infinite number of terms. \ If we don't say whether it is a finite or infinite sequence, we normally mean an infinite sequence. \end{definition} \FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf}{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.6126";cropright "1";cropbottom "0.3874";filename 'graphics/maroon0.wmf';file-properties "XNPEU";}} \begin{example} Each of the following lists is a sequence: \end{example} \begin{center} \begin{tabular}{llll} 1. & $1,2,3,4,5,\cdots $ & The counting numbers. & An infinite sequence. \\ 2. & $10,9,8,7,6,5,4,3,2,1,0$ & Blast Off! & A finite sequence. \\ 3. & $3,1,4,1,5,9,2,6,5,3,\cdots $ & The digits of $\pi $. & An infinite sequence. \\ 4. & $1,\dfrac{1}{2},\dfrac{1}{4},\dfrac{1}{8},\dfrac{1}{16},\dfrac{1}{32}% ,\cdots $ & Keep halving. & An infinite sequence.% \end{tabular} \end{center} \FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf}{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.6126";cropright "1";cropbottom "0.3874";filename 'graphics/maroon0.wmf';file-properties "XNPEU";}} \vspace{1pt} \vspace{1pt}In general, we denote the terms of a sequence as a letter with an integer subscript: \qquad $a_{1},a_{2},a_{3},a_{4},\cdots $ and we frequently give a formula for the $n^{\text{th}}$ term. \ For example, the terms of the sequence, \ $b_{n}=\dfrac{1}{2n+1}$ \ for $% n=1,2,3,\cdots $\ are \qquad $b_{1}=\dfrac{1}{3},\;b_{2}=\dfrac{1}{5},\;b_{3}=\dfrac{1}{7},\;b_{4}=% \dfrac{1}{9},\;\cdots $ Normally the terms are counted starting from $n=1$, as above, but they can start from any number: \vspace{1pt}Remark: Another definition of a sequence is \begin{definition} A \emph{sequence} is a set of numbers which has a one-to-one correspondence with the natural numbers. \end{definition} \paragraph{\protect\vspace{1pt}} \begin{exercise} Write out the first $5$ terms of the sequence $a_{n}=\dfrac{n}{n-1}$ for $% n=2,3,4,\cdots \;$\dotfill \CustomNote[\hyperref{\TCIIcon{BITMAPSETAnswer}{0.1609in}{0.1487in}{0in}}{}{% }{}]{Margin Hint}{$a_{n}=\dfrac{n}{n-1}$ for $n=2,3,4,\cdots $% \par $a_{2}=\dfrac{2}{1},\;a_{3}=\dfrac{3}{2},\;a_{4}=\dfrac{4}{3},\;a_{5}=\dfrac{% 5}{4},\;a_{6}=\dfrac{6}{5}\;\cdots $% \par \vspace{1pt} \par Why did we start from $n=2$?} \end{exercise} \vspace{1pt} To indicate an entire sequence, we enclose the general term in braces: \ $% \left\{ a_{n}\right\} $ \ If necessary, we can also indicate the range of the index: \ $\left\{ a_{n}\right\} \rule[-0.05in]{0in}{0.18in}% _{n=1}^{\infty }$ \ For example, the sequence in the preceding example would be denoted $\left\{ \dfrac{n}{n-1}\right\} _{n=2}^{\infty }$. \FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf}{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.5008";cropright "1";cropbottom "0.4992";filename 'graphics/maroon0.wmf';file-properties "XNPEU";}} \begin{center} \vspace{1pt} \end{center} \paragraph{\textbf{Examples and Notations:}} $\{a_{n}\}_{n=m}^{\infty }$ denotes the sequence starting at $a_{m}$. Thus \begin{equation*} {\Large \{}\frac{1}{2^{n}}{\Large \}}_{n=2}^{\infty }{\Large =}\left\{ \frac{% 1}{4}{\Large ,}\frac{1}{8}{\Large ,}\frac{1}{16}{\Large ,...}\right\} \end{equation*} \begin{equation*} {\Large \{}\frac{(-1)^{n}}{n!}{\Large \}}_{n=3}^{\infty }{\Large =}\left\{ \frac{-1}{3!}{\Large ,}\frac{1}{4!}{\Large ,}\frac{-1}{5!}{\Large ,...}% \right\} \end{equation*} Not all sequences can be defined in the above manner. \ For example, let $% a_{n}$ be the digit in the $n^{th}$ decimal place of the number $\pi $. \ Then $\{a_{n}\}_{n=1}^{\infty }$ is a sequence whose first few terms are $% \{1,4,1,5,9,...\}$. \textbf{Definition:} \ A \emph{sequence} is a set of numbers which has a one-to-one correspondence with the natural numbers. \vspace{1pt}\vspace{0in}\FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf% }{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.1232";cropright "1";cropbottom "0.8768";filename 'graphics/maroon0.wmf';file-properties "XNPEU";}} \subsection{ Limits} \vspace{0in} The limit of the sequence $a_{n}$, denoted $\lim\limits_{n\rightarrow \infty }a_{n}$, \ tells what number the terms are approaching as we go further and further out in the sequence (as $n$ gets arbitrarily large.) \begin{tabular}{l} For example, the plot of the \\ sequence $a_{n}=\dfrac{2n+1}{n}$\ is\quad $\Longrightarrow $ \\ As $n$ gets larger, the terms $a_{n}$ \\ are approaching $2$. \ So we \\ write \\ $\quad \lim\limits_{n\rightarrow \infty }a_{n}=\lim\limits_{n\rightarrow \infty }\dfrac{2n+1}{n}=2$.% \end{tabular} \allowbreak \FRAME{itbpF}{3.039in}{2.0358in}{1.0032in}{}{}{lim1.wmf}{\special% {language "Scientific Word";type "GRAPHIC";maintain-aspect-ratio TRUE;display "PICT";valid_file "F";width 3.039in;height 2.0358in;depth 1.0032in;original-width 217.625pt;original-height 145.125pt;cropleft "0";croptop "1";cropright "1";cropbottom "0";filename 'graphics/lim1.wmf';file-properties "XNPEU";}} \FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf}{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.6126";cropright "1";cropbottom "0.3874";filename 'graphics/maroon3.wmf';file-properties "XNPEU";}} When we are given a sequence, the typical questions we ask are: ``Does the sequence have a limit?'' \ ``If so, what is the limit of the sequence?'' \ \ For now and for most purposes, the following will suffice: \vspace{1pt} \begin{definition} The sequence \emph{has a limit} if the terms $a_{n}$ get closer and closer to a \textsl{finite} number $L$ as $n$ gets arbitrarily large. \ In that case, we say $L$ is the limit and we write $\lim\limits_{n\rightarrow \infty }a_{n}=L$. If a sequence has a limit $L$, we say it is \emph{convergent} and that it \emph{converges to} $L$. If a sequence does not have a limit, we say it is \emph{divergent} or that it \emph{diverges}. \end{definition} \vspace{1pt} If the sequence does not have a limit, it may still have an infinite limit. \ \vspace{1pt} \begin{definition} If the terms $a_{n}$ get\emph{\ arbitrarily large and positive} as $n$ gets arbitrarily large, then we say the limit is \emph{positive infinity} and write $\lim\limits_{n\rightarrow \infty }a_{n}=\infty $. \ We also say the sequence \emph{diverges to} $\infty $.\qquad \fbox{\underline{% \CustomNote[Example]{Margin Hint}{% The sequence $a_{n}=1+\sqrt{n}$ diverges to $\infty $ because $1+\sqrt{n}$ gets arbitrarily large and positive as $n$ gets large. \ Its plot is: \par \qquad \FRAME{itbpF}{2.0358in}{2.0358in}{0in}{}{}{lim2.wmf}{\special% {language "Scientific Word";type "GRAPHIC";maintain-aspect-ratio TRUE;display "PICT";valid_file "F";width 2.0358in;height 2.0358in;depth 0in;original-width 0pt;original-height 0pt;cropleft "0";croptop "1";cropright "1";cropbottom "0";filename 'graphics/lim2.wmf';file-properties "XNPEU";}}}}} If the terms $a_{n}$ get \emph{arbitrarily large and negative} as $n$ gets arbitrarily large, then we say the limit is \emph{negative infinity} and write $\lim\limits_{n\rightarrow \infty }a_{n}=-\infty $. \ We also say the sequence \emph{diverges to} $-\infty $.\qquad \fbox{\underline{% \CustomNote[Example]{Margin Hint}{% The sequence $a_{n}=1-\sqrt{n}$ diverges to $-\infty $ because $1-\sqrt{n}$ gets arbitrarily large and negative as $n$ gets large. \ Its plot is: \par \qquad \FRAME{itbpF}{2.0358in}{2.0358in}{0in}{}{}{lim3.wmf}{\special% {language "Scientific Word";type "GRAPHIC";maintain-aspect-ratio TRUE;display "PICT";valid_file "F";width 2.0358in;height 2.0358in;depth 0in;original-width 0pt;original-height 0pt;cropleft "0";croptop "1";cropright "1";cropbottom "0";filename 'graphics/lim3.wmf';file-properties "XNPEU";}}}}} \end{definition} \vspace{1pt} To say that the limit is positive or negative infinity does \textsl{not} say that the limit exists! \ It merely says the \textsl{way} in which it does not exist, i.e. the \textsl{way} in which it \textsl{diverges}. \vspace{1pt} \textsl{Note:} \ It is certainly possible to diverge without diverging to $% \infty $ or $-\infty $.\qquad \fbox{\underline{% \CustomNote[Example]{Margin Hint}{% The sequence $a_{n}=\left( -1\right) ^{n}+\dfrac{1}{n}$ has the plot \par \FRAME{itbpF}{3.5405in}{1.5333in}{0in}{}{}{lim4.wmf}{\special{language "Scientific Word";type "GRAPHIC";maintain-aspect-ratio TRUE;display "PICT";valid_file "F";width 3.5405in;height 1.5333in;depth 0in;original-width 0pt;original-height 0pt;cropleft "0";croptop "1";cropright "1";cropbottom "0";filename 'graphics/lim4.wmf';file-properties "XNPEU";}} \par Since the terms oscillate between numbers which get closer to $1$ and numbers which get closer to $-1$, the sequence does not converge; it diverges. \ However, it does not diverge to $\infty $ or $-\infty $. \ We say it is \emph{oscillatory divergent}.}}} \FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf}{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.6126";cropright "1";cropbottom "0.3874";filename 'graphics/maroon3.wmf';file-properties "XNPEU";}} \vspace{1pt} In general, the process of finding the limit of a sequence is essentially the same as finding the limit of a continuous function or finding its horizontal asymptote. \ Examples appear on subsequent pages. \subsection{\protect\vspace{0in}Precise Definition of Limits} \vspace{0in} We previously said that $\lim\limits_{n\rightarrow \infty }a_{n}=L$ means that the terms $a_{n}$ get arbitrarily close to a\ finite number $L$ as $n$ gets arbitrarily large. \ We now make this more precise by explaining the use of the word ``arbitrarily.'' \ The idea we want is: if we specify how close to $L$ the terms $a_{n}$ should be (called an \emph{output tolerance}) then for the part of the sequence beyond some point (called a \emph{tail of the sequence}), the terms are all within that tolerance. \ The output tolerance is denoted by epsilon $\left( \varepsilon \right) $ and the tail of the sequence begins with some term $a_{N}$ whose index is $n=N$. \vspace{1pt} \begin{definition} We say the \emph{limit} of the sequence $\left\{ a_{n}\right\} $ \emph{exists% } and is \emph{equal to} a \textsl{finite} number $L$ and we write\qquad $% \lim\limits_{n\rightarrow \infty }a_{n}=L$\qquad to mean: \qquad \qquad For all $\varepsilon >0$, there is an integer $N$ such that \emph{if} $n\geq N$ \emph{then} $\left| a_{n}-L\right| <\varepsilon $% .\medskip If a sequence has a limit $L$, we say it is \emph{convergent} and that it \emph{converges to} $L$. If a sequence does not have a limit, we say it is \emph{divergent} or that it \emph{diverges}. \end{definition} \FRAME{dtbpF}{4.2653in}{0.0701in}{0pt}{}{}{maroon.wmf}{\special{language "Scientific Word";type "GRAPHIC";display "PICT";valid_file "F";width 4.2653in;height 0.0701in;depth 0pt;original-width 290.5625pt;original-height 1pt;cropleft "0";croptop "0.6126";cropright "1";cropbottom "0.3874";filename 'graphics/maroonD.wmf';file-properties "XNPEU";}} \vspace{1pt} We also need a precise definition of an infinite limit. \ The idea here is that the terms $a_{n}$ get larger than any specified number $M$\ and after some point the terms stay larger than $M$. \vspace{1pt} \begin{definition} We say the limit of the sequence $\left\{ a_{n}\right\} $ is \emph{positive infinity} and we write\qquad $\lim\limits_{n\rightarrow \infty }a_{n}=\infty $\qquad to mean: \qquad \qquad For all $M>0$, there is an integer $N$ such that \emph{if} $% n\geq N$ \emph{then} $a_{n}>M$.\medskip We say the limit of the sequence $\left\{ a_{n}\right\} $ is \emph{negative infinity} and we write\qquad $\lim\limits_{n\rightarrow \infty }a_{n}=-\infty $\qquad to mean: \qquad \qquad For all $M<0$, there is an integer $N$ such that \emph{if} $% n\geq N$ \emph{then} $a_{n}