(************** Content-type: application/mathematica ************** CreatedBy='Mathematica 4.2' Mathematica-Compatible Notebook This notebook can be used with any Mathematica-compatible application, such as Mathematica, MathReader or Publicon. The data for the notebook starts with the line containing stars above. To get the notebook into a Mathematica-compatible application, do one of the following: * Save the data starting with the line of stars above into a file with a name ending in .nb, then open the file inside the application; * Copy the data starting with the line of stars above to the clipboard, then use the Paste menu command inside the application. Data for notebooks contains only printable 7-bit ASCII and can be sent directly in email or through ftp in text mode. Newlines can be CR, LF or CRLF (Unix, Macintosh or MS-DOS style). 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Laboratory Objectives\n\tUse ", StyleBox["Mathematica", FontSlant->"Italic"], " to explore\n\t\tPower Series\n\t\tUsing the Ratio Test in Mathematica\n\t\ \tGraphing Power Series partial sums" }], "Text"], Cell[TextData[StyleBox["II. Formatting and Syntax Information", "Text"]], \ "Text"], Cell[TextData[{ Cell[BoxData[ \(InequalitySolve[f[x] < 1, \ x]\)]], " This solves inequalities. It's nifty.\n\t\t\t\t\t\n", StyleBox["PlotStyle\[Rule]RGBColor[1,0,0]\t", FontFamily->"Courier"], "Use this in any Plot[ ] command.\n\t\t\t\t\tMakes graphs in different \ colors." }], "Text", FontFamily->"Helvetica", FontSize->14], Cell[TextData[StyleBox["Power Series", FontWeight->"Bold", FontColor->RGBColor[0, 0, 1]]], "Subtitle"], Cell[TextData[{ StyleBox["The general form for a Power Series about the point x = a:", "Text", FontFamily->"Times", FontSize->14], "\n\n ", Cell[BoxData[ \(TraditionalForm\`\[Sum]\+\(n = 0\)\%\[Infinity]\(\( c\_n\)(x - \ a)\)\^n\)]], "\n \n", StyleBox[" This is an infinite polynomial written in terms of powers of (x \ - a).", "Text", FontFamily->"Times", FontSize->14] }], "Section"], Cell[TextData[{ StyleBox["Given a function, expanding it into a power series can be hard to \ do. This lab will explore several tricks for doing this.\n\n", FontSize->14], StyleBox["Trick 1: Use geometric series.", "Section", FontColor->RGBColor[0, 0, 1]], StyleBox["\nIf the power series is in the form of a geometric series a ", FontSize->14], Cell[BoxData[ FormBox[ StyleBox[\(\(\(+\ ar\)\ + \ ar\^2 + \ ar\^3 + ... \)\(\ \)\), FontSize->14], TraditionalForm]]], StyleBox["then we can just use the formula for a convergent geometric \ series: ", FontSize->14], Cell[BoxData[ FormBox[ StyleBox[\(\(a\/\(1 - r\)\)\(.\)\), "Text", FontSize->14, FontSlant->"Italic"], TraditionalForm]]], "\n\n", StyleBox["In other words, we know that\n", FontSize->16], Cell[BoxData[ \(TraditionalForm\`1\ + \ x\ + \ x\^2\ + \ x\^3\ + \ x\^4 + \ ... \ = \ 1\/\(1 - x\)\)], FontSize->14], StyleBox[" for ", FontSize->14], Cell[BoxData[ \(TraditionalForm\`\(\(|\)\(x\)\(|\)\(\(\[LessEqual]\)\(\ \ \)\(1\)\)\)\)], FontSize->14], StyleBox[". \n", FontSize->14], StyleBox["Example: ", FontSize->16, FontWeight->"Bold"], StyleBox[" what is the power series expansion of ", FontSize->14], Cell[BoxData[ \(TraditionalForm\`2\/\(1 + x\/4\)\)], FontSize->14], StyleBox["? Well, write it as ", FontSize->14], Cell[BoxData[ \(TraditionalForm\`2\/\(1 - \((\(-\(x\/4\)\))\)\)\)], FontSize->14], StyleBox["and then we can see that ", FontSize->14], StyleBox["a = 2", FontSize->14, FontSlant->"Italic"], StyleBox[" and ", FontSize->14], StyleBox["r = -", FontSize->14, FontSlant->"Italic"], Cell[BoxData[ \(TraditionalForm\`x\/4\)]], StyleBox[". So...", FontSize->14] }], "Text", TextAlignment->Left, TextJustification->0], Cell[BoxData[ \(\(\(\[IndentingNewLine]\)\(Simplify[ 2\/\(1 + x\/4\)] == \[Sum]\+\(n = 0\)\%\[Infinity] 2 \((\(-\(x\/4\)\))\)\^n\)\)\)], "Input"], Cell[TextData[{ StyleBox["Evaluate the above expression. The double equal sign \"==\" is a \ command that asks ", FontSize->14], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic"], StyleBox[", \"Is this true?\" ", FontSize->14], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic"], StyleBox[" will respond \"True\" or \"False\". So this can be a great way \ to check if your power series expansion is correct. (It's a good idea to put \ the Simplify[] command in there to make sure the Left-Hand-Side is as simple \ as possible.)", FontSize->14] }], "Text"], Cell[TextData[{ "\n", StyleBox["Trick 2: Finding the radius and interval of convergence:", "Section", FontSize->16, FontColor->RGBColor[0, 0, 1]], StyleBox["\nYou can find the radius of convergence of power series by hand, \ but you can also make ", FontSize->16], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic"], StyleBox[" do it for you using the Ratio Test. Here's how: we'll find the \ interval of convergence for the series ", FontSize->14], Cell[BoxData[ \(\[Sum]\+\(n = 0\)\%\[Infinity] 2 \((\(-x\)/4)\)\^n\)], FontSize->14], StyleBox["that we saw above. \n\nIn preparation for using the Ratio Test, \ let's define the nth term of the series ", FontSize->14], Cell[BoxData[ \(TraditionalForm\`a\_n\)], FontSize->14] }], "Text"], Cell[BoxData[ \(\(\(a[n_, x_] = 2 \((\(-\(x\/4\)\))\)^n\)\(\[IndentingNewLine]\) \)\)], "Input"], Cell[TextData[{ StyleBox["Now we can form the ratio of ", FontSize->14], Cell[BoxData[ \(TraditionalForm\`a\_\(n + 1\)\/a\_\(\(n\)\(\ \)\)\)], FontSize->14], StyleBox["giving it the name \"ratio.\"", FontSize->14], "\n" }], "Text"], Cell[BoxData[ \(\(\(\[IndentingNewLine]\)\(ratio = a[n + 1, x]\/a[n, x]\)\)\)], "Input"], Cell[TextData[{ "\n", StyleBox["Next take the limit of this ratio as n\[Rule] \[Infinity].", FontSize->14] }], "Text"], Cell[BoxData[ \(\(\(\[IndentingNewLine]\)\(Limit[ratio, n \[Rule] \[Infinity]]\)\)\)], "Input"], Cell[TextData[{ StyleBox["By the Ratio Test, the series will converge when the ", FontSize->14], StyleBox["Absolute Value", FontSize->14, FontWeight->"Bold"], StyleBox[" of this answer is less than 1. To solve the inequality ", FontSize->14], Cell[BoxData[ \(Abs[\(-x\)\/4]\)]], StyleBox[" < 1, we must load the package \"Inequality Solve\" in the \ Algebra package. This is done below.", FontSize->14] }], "Text"], Cell[BoxData[ \(\(\(\[IndentingNewLine]\)\(<< Algebra`InequalitySolve`\)\)\)], "Input"], Cell[TextData[{ "\n", StyleBox["To solve the inequality we use the syntax below:", FontSize->14] }], "Text"], Cell[BoxData[ \(\(\(\[IndentingNewLine]\)\(InequalitySolve[Abs[\(-\(x\/4\)\)] < 1, x]\)\)\)], "Input"], Cell[TextData[{ "\n", StyleBox["So now we know that ", FontSize->16], Cell[BoxData[ \(2\/\(1 + x\/4\) = \ \[Sum]\+\(n = 0\)\%\[Infinity] 2 \((\(-\(x\/4\)\))\)\^n\)], FontSize->14], StyleBox[" is a convergent power series expansion on the interval -4 < x < \ 4. We DON\"T know what is happening at the end points, at x = -4 and at x = \ 4. You would have to check these separately by hand.\n\nWe can also check \ our work by making a plot of our original function with a partial sum of our \ power series. I like to use the command PlotStyle->{RGBColor[0,0,0], \ RGBColor[1,0,0] ...} to make the graphs on the same axis in different colors. \ [0,0,0] is black, [1,0,0] is red, and you can experiment with others. So, \ to check out power series and interval of convergence for ", FontSize->14], Cell[BoxData[ \(2\/\(1 + x\/4\)\)], FontSize->14], StyleBox[" we can try graphing it with, say, the 6th partial sum:", FontSize->14] }], "Text"], Cell[BoxData[ \(\(\(\[IndentingNewLine]\)\(Plot[{2\/\(1 + x\/4\), \ \[Sum]\+\(n = \ 0\)\%6 2 \((\(-\(x\/4\)\))\)\^n}, \ {x, \(-5\), 5}, \[IndentingNewLine]PlotStyle \[Rule] {RGBColor[0, 0, 0], \ RGBColor[1, 0, 0]}]\)\)\)], "Input"], Cell[TextData[{ "\n", StyleBox["If the graphs look like they line up inside -4 < x < 4, then \ we're lookin' good! (Try a higher partial sum, like the forst 10 terms, to \ make it even more accurate.)", FontSize->16] }], "Text"], Cell[TextData[{ "\n", StyleBox["Question 1:", FontSize->16, FontWeight->"Bold", FontColor->RGBColor[1, 0, 0]], StyleBox[" Consider the function ", FontSize->16, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`5\/\(3 - x\)\)], FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox[".\n(a) Find the values of a and r in the geometric series \ representation of this ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["(", FontSize->16, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`a\/\(1 - r\)\)], FontSize->16, FontColor->RGBColor[1, 0, 0]], StyleBox["=", FontSize->16, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ FormBox[ RowBox[{\(\[Sum]\+\(n = 0\)\%\[Infinity]\), SuperscriptBox[ StyleBox[ RowBox[{ StyleBox["a", FontSlant->"Italic"], "r"}]], "n"]}], TraditionalForm]], FontSize->16, FontColor->RGBColor[1, 0, 0]], StyleBox[")", FontSize->16, FontColor->RGBColor[1, 0, 0]], StyleBox[" and write the power series representation. (Hint: factor out a \ 1/3.) Use ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic", FontColor->RGBColor[1, 0, 0]], StyleBox[" to check your work.", FontSize->14, FontColor->RGBColor[1, 0, 0]] }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ "\n", StyleBox["(b) Use the Ratio Test in ", FontSize->16, FontColor->RGBColor[1, 0, 0]], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic", FontColor->RGBColor[1, 0, 0]], StyleBox[" to find the interval of convergence of this power series.", FontSize->14, FontColor->RGBColor[1, 0, 0]] }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ StyleBox["(c) Make a pretty plot (with color!) of the original function \ together with the 8th partial sum.", FontSize->14, FontColor->RGBColor[1, 0, 0]], "\n" }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ "\n", StyleBox["Trick 3: Use derivatives!", "Section", FontColor->RGBColor[0, 0, 1]], "\n\n", StyleBox["Question 2:", FontSize->16, FontWeight->"Bold", FontColor->RGBColor[1, 0, 0]], StyleBox[" (a) Find a power series expansion for ", FontSize->16, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`1\/\((1 - x)\)\^2\)], FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox[". Write your answer in summation notation and use ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic", FontColor->RGBColor[1, 0, 0]], StyleBox[" to check if it's true. ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["Hint: ", FontSize->14, FontWeight->"Bold", FontColor->RGBColor[1, 0, 0]], StyleBox[" Use ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic", FontColor->RGBColor[1, 0, 0]], StyleBox[" to remind yourself what the derivative of ", FontSize->14, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`1\/\(1 - x\)\)], FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["is. (Recall that ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["D[f[x],x]", "Input", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox[" will give you the derivative of f[x] with respect to x.) And \ remember that ", FontSize->14, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`1\/\(1 - x\) = \[Sum]\+\(n = 0\)\%\[Infinity] \ x\^n\)], FontSize->16, FontColor->RGBColor[1, 0, 0]], StyleBox["for ", FontSize->16, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`\(\(|\)\(x\)\(|\)\(\(<\)\(\ \)\(1\)\)\)\)], FontSize->16, FontColor->RGBColor[1, 0, 0]], StyleBox[".", FontSize->16, FontColor->RGBColor[1, 0, 0]] }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ StyleBox["(b) Find the radius of convergence of this power series.", FontSize->14, FontColor->RGBColor[1, 0, 0]], "\n" }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ "\n", StyleBox["Trick 4: Use antiderivatives!", "Section", FontColor->RGBColor[0, 0, 1]], "\n\n", StyleBox["Question 3: ", FontSize->14, FontWeight->"Bold", FontColor->RGBColor[1, 0, 0]], StyleBox[" (a) Find a power series expansion of ln(1+x), writing your \ answer in summation notation. Hint: What's the derivative of Log[1+x]? \ Look kinda familiar? You can write this in summation notation (only do the \ first 5 terms or so) and then find the antiderivative (using the \ Integrate[f[x],x] command) to get the power series of the original.", FontSize->14, FontColor->RGBColor[1, 0, 0]] }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ StyleBox["(b) Make a pretty plot (using colors) of Log[1+x] together with \ some of the partial sums of its power series using the range {x, -1, 2}. Be \ sure to indicate which colors correspond to which functions!", FontSize->14, FontColor->RGBColor[1, 0, 0]], "\n" }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ StyleBox["Question 4: Name that Power Series:", FontSize->14, FontWeight->"Bold", FontColor->RGBColor[1, 0, 0]], StyleBox["\nConsider the power series ", FontSize->14, FontColor->RGBColor[1, 0, 0]], Cell[BoxData[ \(TraditionalForm\`\[Sum]\+\(n = 0\)\%\[Infinity] x\^n\/\(n!\)\)], FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox[".\n(a) Use ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["Mathematica", FontSize->14, FontSlant->"Italic", FontColor->RGBColor[1, 0, 0]], StyleBox[" and the Ratio Test to compute the interval of convergence of \ this power series. WARNING: you may need to use the ", FontSize->14, FontColor->RGBColor[1, 0, 0]], StyleBox["FullSimplify[ ]", "Input"], StyleBox[" command to make the factorials cancel. ", FontSize->14, FontColor->RGBColor[1, 0, 0]] }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ StyleBox["(b) Make a nice plot of some high-termed partial sums of this \ power series. What function does it look like the series is converging to?", FontSize->14, FontColor->RGBColor[1, 0, 0]], "\n" }], "Text"], Cell[BoxData[ \(\[IndentingNewLine]\)], "Input"], Cell[TextData[{ StyleBox["Now that you're done, ", FontSize->18], "\n\t(1) \t", StyleBox["Clean up your work", FontWeight->"Bold"], " by deleting everything that's not needed. \n\t\tThere should only be the \ title, your names, section number, and the questions and your answers\n\t\t\ (with any needed explanations, graphs, etc.).\n\t(2) \tSave this to your \ disk.\n\t(3)\tGo back to Blackboard and upload your final lab report to the \ ", StyleBox["Digital Drop Box", FontWeight->"Bold"], ", located\n\t\tin the ", StyleBox["User Tools", FontWeight->"Bold"], " area. Remember that you have to first ", StyleBox["ADD", FontWeight->"Bold"], " your file to your digital drop box and \n\t\tthen ", StyleBox["SEND it to me!", FontWeight->"Bold"] }], "Text", CellFrame->{{0, 0}, {0, 2}}, FontSize->12] }, FrontEndVersion->"4.2 for Macintosh", ScreenRectangle->{{0, 800}, {0, 580}}, CellGrouping->Manual, WindowSize->{683, 477}, WindowMargins->{{9, Automatic}, {Automatic, 21}}, PrintingCopies->1, PrintingPageRange->{1, Automatic}, MacintoshSystemPageSetup->"\<\ 00<0004/0B`000002mT8o?mooh<" ] (******************************************************************* Cached data follows. If you edit this Notebook file directly, not using Mathematica, you must remove the line containing CacheID at the top of the file. 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