# 1.1 Parametric equations  (Page 5/14)

 Page 5 / 14 Graph of various hypocycloids corresponding to different values of a / b .

## The witch of agnesi

Many plane curves in mathematics are named after the people who first investigated them, like the folium of Descartes or the spiral of Archimedes. However, perhaps the strangest name for a curve is the witch of Agnesi . Why a witch?

Maria Gaetana Agnesi (1718–1799) was one of the few recognized women mathematicians of eighteenth-century Italy. She wrote a popular book on analytic geometry, published in 1748, which included an interesting curve that had been studied by Fermat in 1630. The mathematician Guido Grandi showed in 1703 how to construct this curve, which he later called the “versoria,” a Latin term for a rope used in sailing. Agnesi used the Italian term for this rope, “versiera,” but in Latin, this same word means a “female goblin.” When Agnesi’s book was translated into English in 1801, the translator used the term “witch” for the curve, instead of rope. The name “witch of Agnesi” has stuck ever since.

The witch of Agnesi is a curve defined as follows: Start with a circle of radius a so that the points $\left(0,0\right)$ and $\left(0,2a\right)$ are points on the circle ( [link] ). Let O denote the origin. Choose any other point A on the circle, and draw the secant line OA . Let B denote the point at which the line OA intersects the horizontal line through $\left(0,2a\right).$ The vertical line through B intersects the horizontal line through A at the point P . As the point A varies, the path that the point P travels is the witch of Agnesi curve for the given circle.

Witch of Agnesi curves have applications in physics, including modeling water waves and distributions of spectral lines. In probability theory, the curve describes the probability density function of the Cauchy distribution. In this project you will parameterize these curves. As the point A moves around the circle, the point P traces out the witch of Agnesi curve for the given circle.
1. On the figure, label the following points, lengths, and angle:
1. C is the point on the x -axis with the same x -coordinate as A .
2. x is the x -coordinate of P , and y is the y -coordinate of P .
3. E is the point $\left(0,a\right).$
4. F is the point on the line segment OA such that the line segment EF is perpendicular to the line segment OA .
5. b is the distance from O to F .
6. c is the distance from F to A .
7. d is the distance from O to B .
8. $\theta$ is the measure of angle $\text{∠}COA.$

The goal of this project is to parameterize the witch using $\theta$ as a parameter. To do this, write equations for x and y in terms of only $\theta .$
2. Show that $d=\frac{2a}{\text{sin}\phantom{\rule{0.2em}{0ex}}\theta }.$
3. Note that $x=d\phantom{\rule{0.2em}{0ex}}\text{cos}\phantom{\rule{0.2em}{0ex}}\theta .$ Show that $x=2a\phantom{\rule{0.2em}{0ex}}\text{cot}\phantom{\rule{0.2em}{0ex}}\theta .$ When you do this, you will have parameterized the x -coordinate of the curve with respect to $\theta .$ If you can get a similar equation for y , you will have parameterized the curve.
4. In terms of $\theta ,$ what is the angle $\text{∠}EOA?$
5. Show that $b+c=2a\phantom{\rule{0.2em}{0ex}}\text{cos}\left(\frac{\pi }{2}-\theta \right).$
6. Show that $y=2a\phantom{\rule{0.2em}{0ex}}\text{cos}\left(\frac{\pi }{2}-\theta \right)\phantom{\rule{0.2em}{0ex}}\text{sin}\phantom{\rule{0.2em}{0ex}}\theta .$
7. Show that $y=2a\phantom{\rule{0.2em}{0ex}}{\text{sin}}^{2}\theta .$ You have now parameterized the y -coordinate of the curve with respect to $\theta .$
8. Conclude that a parameterization of the given witch curve is
$x=2a\phantom{\rule{0.2em}{0ex}}\text{cot}\phantom{\rule{0.2em}{0ex}}\theta ,y=2a\phantom{\rule{0.2em}{0ex}}{\text{sin}}^{2}\theta ,-\infty <\theta <\infty .$
9. Use your parameterization to show that the given witch curve is the graph of the function $f\left(x\right)=\frac{8{a}^{3}}{{x}^{2}+4{a}^{2}}.$

#### Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
Maciej
characteristics of micro business
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
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Cied
what is biological synthesis of nanoparticles
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Source:  OpenStax, Calculus volume 3. OpenStax CNX. Feb 05, 2016 Download for free at http://legacy.cnx.org/content/col11966/1.2
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