# 6.4 Working with taylor series  (Page 7/11)

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Use ${\left(1+x\right)}^{1\text{/}3}=1+\frac{1}{3}x-\frac{1}{9}{x}^{2}+\frac{5}{81}{x}^{3}-\frac{10}{243}{x}^{4}+\text{⋯}$ with $x=1$ to approximate ${2}^{1\text{/}3}.$

Use the approximation ${\left(1-x\right)}^{2\text{/}3}=1-\frac{2x}{3}-\frac{{x}^{2}}{9}-\frac{4{x}^{3}}{81}-\frac{7{x}^{4}}{243}-\frac{14{x}^{5}}{729}+\text{⋯}$ for $|x|<1$ to approximate ${2}^{1\text{/}3}={2.2}^{-2\text{/}3}.$

Twice the approximation is $1.260\text{…}$ whereas ${2}^{1\text{/}3}=1.2599....$

Find the $25\text{th}$ derivative of $f\left(x\right)={\left(1+{x}^{2}\right)}^{13}$ at $x=0.$

Find the $99$ th derivative of $f\left(x\right)={\left(1+{x}^{4}\right)}^{25}.$

${f}^{\left(99\right)}\left(0\right)=0$

In the following exercises, find the Maclaurin series of each function.

$f\left(x\right)=x{e}^{2x}$

$f\left(x\right)={2}^{x}$

$\sum _{n=0}^{\infty }\frac{{\left(\text{ln}\phantom{\rule{0.1em}{0ex}}\left(2\right)x\right)}^{n}}{n\text{!}}$

$f\left(x\right)=\frac{\text{sin}\phantom{\rule{0.1em}{0ex}}x}{x}$

$f\left(x\right)=\frac{\text{sin}\left(\sqrt{x}\right)}{\sqrt{x}},\phantom{\rule{0.5em}{0ex}}\left(x>0\right),$

For $x>0,\text{sin}\left(\sqrt{x}\right)=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{x}^{\left(2n+1\right)\text{/}2}}{\sqrt{x}\left(2n+1\right)\text{!}}=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{x}^{n}}{\left(2n+1\right)\text{!}}.$

$f\left(x\right)=\text{sin}\left({x}^{2}\right)$

$f\left(x\right)={e}^{{x}^{3}}$

${e}^{{x}^{3}}=\sum _{n=0}^{\infty }\frac{{x}^{3n}}{n\text{!}}$

$f\left(x\right)={\text{cos}}^{2}x$ using the identity ${\text{cos}}^{2}x=\frac{1}{2}+\frac{1}{2}\phantom{\rule{0.1em}{0ex}}\text{cos}\phantom{\rule{0.1em}{0ex}}\left(2x\right)$

$f\left(x\right)={\text{sin}}^{2}x$ using the identity ${\text{sin}}^{2}x=\frac{1}{2}-\frac{1}{2}\phantom{\rule{0.1em}{0ex}}\text{cos}\phantom{\rule{0.1em}{0ex}}\left(2x\right)$

${\text{sin}}^{2}x=\text{−}\sum _{k=1}^{\infty }\frac{{\left(-1\right)}^{k}{2}^{2k-1}{x}^{2k}}{\left(2k\right)\text{!}}$

In the following exercises, find the Maclaurin series of $F\left(x\right)={\int }_{0}^{x}f\left(t\right)\phantom{\rule{0.1em}{0ex}}dt$ by integrating the Maclaurin series of $f$ term by term. If $f$ is not strictly defined at zero, you may substitute the value of the Maclaurin series at zero.

$F\left(x\right)={\int }_{0}^{x}{e}^{\text{−}{t}^{2}}dt;f\left(t\right)={e}^{\text{−}{t}^{2}}=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{t}^{2n}}{n\text{!}}$

$F\left(x\right)={\text{tan}}^{-1}x;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\frac{1}{1+{t}^{2}}=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}{t}^{2n}$

${\text{tan}}^{-1}x=\sum _{k=0}^{\infty }\frac{{\left(-1\right)}^{k}{x}^{2k+1}}{2k+1}$

$F\left(x\right)={\text{tanh}}^{-1}x;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\frac{1}{1-{t}^{2}}=\sum _{n=0}^{\infty }{t}^{2n}$

$F\left(x\right)={\text{sin}}^{-1}x;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\frac{1}{\sqrt{1-{t}^{2}}}=\sum _{k=0}^{\infty }\left(\begin{array}{c}\frac{1}{2}\hfill \\ k\hfill \end{array}\right)\frac{{t}^{2k}}{k\text{!}}$

${\text{sin}}^{-1}x=\sum _{n=0}^{\infty }\left(\begin{array}{c}\frac{1}{2}\hfill \\ n\hfill \end{array}\right)\frac{{x}^{2n+1}}{\left(2n+1\right)n\text{!}}$

$F\left(x\right)={\int }_{0}^{x}\frac{\text{sin}\phantom{\rule{0.1em}{0ex}}t}{t}dt;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\frac{\text{sin}\phantom{\rule{0.1em}{0ex}}t}{t}=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{t}^{2n}}{\left(2n+1\right)\text{!}}$

$F\left(x\right)={\int }_{0}^{x}\text{cos}\left(\sqrt{t}\right)\phantom{\rule{0.1em}{0ex}}dt;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{x}^{n}}{\left(2n\right)\text{!}}$

$F\left(x\right)=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{x}^{n+1}}{\left(n+1\right)\left(2n\right)\text{!}}$

$F\left(x\right)={\int }_{0}^{x}\frac{1-\text{cos}\phantom{\rule{0.1em}{0ex}}t}{{t}^{2}}dt;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\frac{1-\text{cos}\phantom{\rule{0.1em}{0ex}}t}{{t}^{2}}=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{t}^{2n}}{\left(2n+2\right)\text{!}}$

$F\left(x\right)={\int }_{0}^{x}\frac{\text{ln}\phantom{\rule{0.1em}{0ex}}\left(1+t\right)}{t}dt;\phantom{\rule{0.5em}{0ex}}f\left(t\right)=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}\frac{{t}^{n}}{n+1}$

$F\left(x\right)=\sum _{n=1}^{\infty }{\left(-1\right)}^{n+1}\frac{{x}^{n}}{{n}^{2}}$

In the following exercises, compute at least the first three nonzero terms (not necessarily a quadratic polynomial) of the Maclaurin series of $f.$

$f\left(x\right)=\text{sin}\left(x+\frac{\pi }{4}\right)=\text{sin}\phantom{\rule{0.1em}{0ex}}x\phantom{\rule{0.1em}{0ex}}\text{cos}\left(\frac{\pi }{4}\right)+\text{cos}\phantom{\rule{0.1em}{0ex}}x\phantom{\rule{0.1em}{0ex}}\text{sin}\left(\frac{\pi }{4}\right)$

$f\left(x\right)=\text{tan}\phantom{\rule{0.1em}{0ex}}x$

$x+\frac{{x}^{3}}{3}+\frac{2{x}^{5}}{15}+\text{⋯}$

$f\left(x\right)=\text{ln}\phantom{\rule{0.1em}{0ex}}\left(\text{cos}\phantom{\rule{0.1em}{0ex}}x\right)$

$f\left(x\right)={e}^{x}\text{cos}\phantom{\rule{0.1em}{0ex}}x$

$1+x-\frac{{x}^{3}}{3}-\frac{{x}^{4}}{6}+\text{⋯}$

$f\left(x\right)={e}^{\text{sin}\phantom{\rule{0.1em}{0ex}}x}$

$f\left(x\right)={\text{sec}}^{2}x$

$1+{x}^{2}+\frac{2{x}^{4}}{3}+\frac{17{x}^{6}}{45}+\text{⋯}$

$f\left(x\right)=\text{tanh}\phantom{\rule{0.1em}{0ex}}x$

$f\left(x\right)=\frac{\text{tan}\sqrt{x}}{\sqrt{x}}$ (see expansion for $\text{tan}\phantom{\rule{0.1em}{0ex}}x\right)$

Using the expansion for $\text{tan}\phantom{\rule{0.1em}{0ex}}x$ gives $1+\frac{x}{3}+\frac{2{x}^{2}}{15}.$

In the following exercises, find the radius of convergence of the Maclaurin series of each function.

$\text{ln}\phantom{\rule{0.1em}{0ex}}\left(1+x\right)$

$\frac{1}{1+{x}^{2}}$

$\frac{1}{1+{x}^{2}}=\sum _{n=0}^{\infty }{\left(-1\right)}^{n}{x}^{2n}$ so $R=1$ by the ratio test.

${\text{tan}}^{-1}x$

$\text{ln}\phantom{\rule{0.1em}{0ex}}\left(1+{x}^{2}\right)$

$\text{ln}\phantom{\rule{0.1em}{0ex}}\left(1+{x}^{2}\right)=\sum _{n=1}^{\infty }\frac{{\left(-1\right)}^{n-1}}{n}{x}^{2n}$ so $R=1$ by the ratio test.

Find the Maclaurin series of $\text{sinh}\phantom{\rule{0.1em}{0ex}}x=\frac{{e}^{x}-{e}^{\text{−}x}}{2}.$

Find the Maclaurin series of $\text{cosh}\phantom{\rule{0.1em}{0ex}}x=\frac{{e}^{x}+{e}^{\text{−}x}}{2}.$

Add series of ${e}^{x}$ and ${e}^{\text{−}x}$ term by term. Odd terms cancel and $\text{cosh}\phantom{\rule{0.1em}{0ex}}x=\sum _{n=0}^{\infty }\frac{{x}^{2n}}{\left(2n\right)\text{!}}.$

Differentiate term by term the Maclaurin series of $\text{sinh}\phantom{\rule{0.1em}{0ex}}x$ and compare the result with the Maclaurin series of $\text{cosh}\phantom{\rule{0.1em}{0ex}}x.$

[T] Let ${S}_{n}\left(x\right)=\sum _{k=0}^{n}{\left(-1\right)}^{k}\frac{{x}^{2k+1}}{\left(2k+1\right)\text{!}}$ and ${C}_{n}\left(x\right)=\sum _{n=0}^{n}{\left(-1\right)}^{k}\frac{{x}^{2k}}{\left(2k\right)\text{!}}$ denote the respective Maclaurin polynomials of degree $2n+1$ of $\text{sin}\phantom{\rule{0.1em}{0ex}}x$ and degree $2n$ of $\text{cos}\phantom{\rule{0.1em}{0ex}}x.$ Plot the errors $\frac{{S}_{n}\left(x\right)}{{C}_{n}\left(x\right)}-\text{tan}\phantom{\rule{0.1em}{0ex}}x$ for $n=1,..,5$ and compare them to $x+\frac{{x}^{3}}{3}+\frac{2{x}^{5}}{15}+\frac{17{x}^{7}}{315}-\text{tan}\phantom{\rule{0.1em}{0ex}}x$ on $\left(-\frac{\pi }{4},\frac{\pi }{4}\right).$

The ratio $\frac{{S}_{n}\left(x\right)}{{C}_{n}\left(x\right)}$ approximates $\text{tan}\phantom{\rule{0.1em}{0ex}}x$ better than does ${p}_{7}\left(x\right)=x+\frac{{x}^{3}}{3}+\frac{2{x}^{5}}{15}+\frac{17{x}^{7}}{315}$ for $N\ge 3.$ The dashed curves are $\frac{{S}_{n}}{{C}_{n}}-\text{tan}$ for $n=1,2.$ The dotted curve corresponds to $n=3,$ and the dash-dotted curve corresponds to $n=4.$ The solid curve is ${p}_{7}-\text{tan}\phantom{\rule{0.1em}{0ex}}x.$

Use the identity $2\phantom{\rule{0.1em}{0ex}}\text{sin}\phantom{\rule{0.1em}{0ex}}x\phantom{\rule{0.1em}{0ex}}\text{cos}\phantom{\rule{0.1em}{0ex}}x=\text{sin}\left(2x\right)$ to find the power series expansion of ${\text{sin}}^{2}x$ at $x=0.$ ( Hint: Integrate the Maclaurin series of $\text{sin}\left(2x\right)$ term by term.)

If $y=\sum _{n=0}^{\infty }{a}_{n}{x}^{n},$ find the power series expansions of $x{y}^{\prime }$ and ${x}^{2}y\text{″}.$

By the term-by-term differentiation theorem, ${y}^{\prime }=\sum _{n=1}^{\infty }n{a}_{n}{x}^{n-1}$ so ${y}^{\prime }=\sum _{n=1}^{\infty }n{a}_{n}{x}^{n-1}\phantom{\rule{0.2em}{0ex}}x{y}^{\prime }=\sum _{n=1}^{\infty }n{a}_{n}{x}^{n},$ whereas ${y}^{\prime }=\sum _{n=2}^{\infty }n\left(n-1\right){a}_{n}{x}^{n-2}$ so $xy\text{″}=\sum _{n=2}^{\infty }n\left(n-1\right){a}_{n}{x}^{n}.$

[T] Suppose that $y=\sum _{k=0}^{\infty }{a}_{k}{x}^{k}$ satisfies ${y}^{\prime }=-2xy$ and $y\left(0\right)=0.$ Show that ${a}_{2k+1}=0$ for all $k$ and that ${a}_{2k+2}=\frac{\text{−}{a}_{2k}}{k+1}.$ Plot the partial sum ${S}_{20}$ of $y$ on the interval $\left[-4,4\right].$

#### Questions & Answers

where we get a research paper on Nano chemistry....?
what are the products of Nano chemistry?
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
I only see partial conversation and what's the question here!
what about nanotechnology for water purification
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
Leaves accumulate on the forest floor at a rate of 2 g/cm2/yr and also decompose at a rate of 90% per year. Write a differential equation governing the number of grams of leaf litter per square centimeter of forest floor, assuming at time 0 there is no leaf litter on the ground. Does this amount approach a steady value? What is that value?
You have a cup of coffee at temperature 70°C, which you let cool 10 minutes before you pour in the same amount of milk at 1°C as in the preceding problem. How does the temperature compare to the previous cup after 10 minutes?
Abdul