diff --git a/ExponentialApproximants.png b/ExponentialApproximants.png new file mode 100644 index 0000000..75a6470 Binary files /dev/null and b/ExponentialApproximants.png differ diff --git a/exponential.tex b/exponential.tex index dc137d2..853c104 100644 --- a/exponential.tex +++ b/exponential.tex @@ -92,14 +92,14 @@ $$ These formulas should be memorized, both in their long polynomial form and their more concise summation notation form. \subsection*{Example} -Use Euler's formula to show that $e^{i \pi}=-1$. Answer +Use Euler's formula to show that $e^{i \pi}=-1$. \hyperref[ExponentialsAnswer1]{Answer} \subsection*{Example} -Compute $1-\frac{\pi^2}{2!}+\frac{\pi^4}{4!}-\cdots$. Answer +Compute $1-\frac{\pi^2}{2!}+\frac{\pi^4}{4!}-\cdots$. \hyperref[ExponentialsAnswer2]{Answer} \subsection*{Example} -Check that taking the derivative of the long polynomial for $\sin x$ gives the long polynomial for $\cos x$ (hence, verify that $\frac{d}{d x} \sin x=\cos x$ ). Answer +Check that taking the derivative of the long polynomial for $\sin x$ gives the long polynomial for $\cos x$ (hence, verify that $\frac{d}{d x} \sin x=\cos x$ ). \hyperref[ExponentialsAnswer3]{Answer} \subsection*{Example} -Show that the long polynomial for $e^x$ satisfies the first property above, namely $e^{x+y}=e^x e^y$. Hint: start with the long polynomials for $e^x$ and $e^y$ and multiply these together, and carefully collect like terms to show it equals the long polynomial for $e^{x+y}$. Answer +Show that the long polynomial for $e^x$ satisfies the first property above, namely $e^{x+y}=e^x e^y$. Hint: start with the long polynomials for $e^x$ and $e^y$ and multiply these together, and carefully collect like terms to show it equals the long polynomial for $e^{x+y}$. \hyperref[ExponentialsAnswer4]{Answer} \section{More on the long polynomial} @@ -114,4 +114,27 @@ $$ \end{aligned} $$ -Each polynomial in the sequence is, in a sense, the best approximation possible of that degree. Put another way, taking the first several terms of the long polynomial gives a good polynomial approximation of the function. The more terms included, the better the approximation. This is how calculators compute the exponential function (without having to add up infinitely many things). \ No newline at end of file +Each polynomial in the sequence is, in a sense, the best approximation possible of that degree. Put another way, taking the first several terms of the long polynomial gives a good polynomial approximation of the function. The more terms included, the better the approximation. This is how calculators compute the exponential function (without having to add up infinitely many things). + +\begin{figure}[h] + \centering + \includegraphics[width=0.7\linewidth]{ExponentialApproximants} +% \caption{} + \label{fig:exponentialapproximants} +\end{figure} + +\section{EXERCISES} +\begin{itemize} + + \item[\textcolor{red}{\tikzcircle{3pt}}] So, how good of an approximation is a polynomial truncation of $e^{\text {? }}$. Use a calculator to compare how close $e$ is to the linear, quadratic, cubic, quartic, and quintic approximations. How many digits of accuracy do you seem to be gaining with each additional term in the series? +\end{itemize} +%- +%- Now, do the same thing with $1 / e$ by plugging in $x=-1$ into the series. Do you have the same results? Are you surprised? +%- Calculate the following sum using what you know: +%$$ +%\sum_{n=0}^{\infty}(-1)^n \frac{(\ln 3)^n}{n!} +%$$ +%- Write out the first four terms of the following series +%$$ +%\sum_{n=0}^{\infty}(-1)^n \frac{\pi^{2 n}}{2^n n!} +%$$ \ No newline at end of file diff --git a/solutions.tex b/solutions.tex index dc65399..bedcbae 100644 --- a/solutions.tex +++ b/solutions.tex @@ -91,9 +91,39 @@ \chapter*{EXPONENTIALS} \section*{Euler's formula} \subsection*{Answer 1} + \label{ExponentialsAnswer1} Setting $x=\pi$ in Euler's formula gives $e^{i \pi}=\cos \pi+i \sin \pi=-1$. -% + + \subsection*{Answer 2} + \label{ExponentialsAnswer2} + Note that this is the long polynomial for $\cos x$, evaluated at $x=\pi$. So the value is $\cos \pi=-1$. + + \subsection*{Answer 3} + \label{ExponentialsAnswer3} + Computing the derivative term by term gives + $$ + \begin{aligned} + \frac{d}{d x} \sin (x) & =\frac{d}{d x}\left(x-\frac{x^3}{3!}+\frac{x^5}{5!}-\ldots\right) \\ + & =1-3 \frac{x^2}{3!}+5 \frac{x^4}{5!}-\ldots \\ + & =1-\frac{x^2}{2!}+\frac{x^4}{4!}-\ldots + \end{aligned} + $$ + which is the long polynomial for $\cos x$, as desired. + + \subsection*{Answer 4} + \label{ExponentialsAnswer4} + Beginning with $e^x \cdot e^y$, we find + $$ + \begin{aligned} + e^x \cdot e^y & =\left(1+x+\frac{x^2}{2!}+\cdots\right)\left(1+y+\frac{y^2}{2!}+\cdots\right) \\ + & =1+(x+y)+\left(\frac{x^2}{2!}+x y+\frac{y^2}{2!}\right)+\cdots \\ + & =1+(x+y)+\frac{x^2+2 x y+y^2}{2!}+\cdots \\ + & =1+(x+y)+\frac{(x+y)^2}{2!}+\cdots, + \end{aligned} + $$ + which is the long polynomial for $e^{x+y}$, as desired. + % \subsection{Euler's Formula} % % \subsection{Additional Examples} diff --git a/upenn.pdf b/upenn.pdf index 105b255..95444e6 100644 Binary files a/upenn.pdf and b/upenn.pdf differ diff --git a/upenn.tex b/upenn.tex index 52746d4..26ec66c 100644 --- a/upenn.tex +++ b/upenn.tex @@ -28,6 +28,14 @@ \setkomafont{disposition}{\normalcolor\bfseries} % alle überschriften fett und serifenlos %\setkomafont{disposition}{\normalcolor} + +\usepackage{tikz} + +\newcommand{\tikzcircle}[2][red,fill=red]{\tikz[baseline=-0.5ex]\draw[#1,radius=#2] (0,0) circle ;}% + + + + \setlength\parindent{0pt} \everymath{\displaystyle}