# 1.5 Conic sections  (Page 4/23)

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Divide both sides by ${a}^{2}-{c}^{2}.$ This gives the equation

$\frac{{x}^{2}}{{a}^{2}}+\frac{{y}^{2}}{{a}^{2}-{c}^{2}}=1.$

If we refer back to [link] , then the length of each of the two green line segments is equal to a . This is true because the sum of the distances from the point Q to the foci $F\phantom{\rule{0.2em}{0ex}}\text{and}\phantom{\rule{0.2em}{0ex}}{F}^{\prime }$ is equal to 2 a , and the lengths of these two line segments are equal. This line segment forms a right triangle with hypotenuse length a and leg lengths b and c . From the Pythagorean theorem, ${a}^{2}+{b}^{2}={c}^{2}$ and ${b}^{2}={a}^{2}-{c}^{2}.$ Therefore the equation of the ellipse becomes

$\frac{{x}^{2}}{{a}^{2}}+\frac{{y}^{2}}{{b}^{2}}=1.$

Finally, if the center of the ellipse is moved from the origin to a point $\left(h,k\right),$ we have the following standard form of an ellipse.

## Equation of an ellipse in standard form

Consider the ellipse with center $\left(h,k\right),$ a horizontal major axis with length 2 a , and a vertical minor axis with length 2 b . Then the equation of this ellipse in standard form is

$\frac{{\left(x-h\right)}^{2}}{{a}^{2}}+\frac{{\left(y-k\right)}^{2}}{{b}^{2}}=1$

and the foci are located at $\left(h±c,k\right),$ where ${c}^{2}={a}^{2}-{b}^{2}.$ The equations of the directrices are $x=h±\frac{{a}^{2}}{c}.$

If the major axis is vertical, then the equation of the ellipse becomes

$\frac{{\left(x-h\right)}^{2}}{{b}^{2}}+\frac{{\left(y-k\right)}^{2}}{{a}^{2}}=1$

and the foci are located at $\left(h,k±c\right),$ where ${c}^{2}={a}^{2}-{b}^{2}.$ The equations of the directrices in this case are $y=k±\frac{{a}^{2}}{c}.$

If the major axis is horizontal, then the ellipse is called horizontal, and if the major axis is vertical, then the ellipse is called vertical. The equation of an ellipse is in general form if it is in the form $A{x}^{2}+B{y}^{2}+Cx+Dy+E=0,$ where A and B are either both positive or both negative. To convert the equation from general to standard form, use the method of completing the square.

## Finding the standard form of an ellipse

Put the equation $9{x}^{2}+4{y}^{2}-36x+24y+36=0$ into standard form and graph the resulting ellipse.

First subtract 36 from both sides of the equation:

$9{x}^{2}+4{y}^{2}-36x+24y=-36.$

Next group the x terms together and the y terms together, and factor out the common factor:

$\begin{array}{ccc}\hfill \left(9{x}^{2}-36x\right)+\left(4{y}^{2}+24y\right)& =\hfill & -36\hfill \\ \hfill 9\left({x}^{2}-4x\right)+4\left({y}^{2}+6y\right)& =\hfill & -36.\hfill \end{array}$

We need to determine the constant that, when added inside each set of parentheses, results in a perfect square. In the first set of parentheses, take half the coefficient of x and square it. This gives ${\left(\frac{-4}{2}\right)}^{2}=4.$ In the second set of parentheses, take half the coefficient of y and square it. This gives ${\left(\frac{6}{2}\right)}^{2}=9.$ Add these inside each pair of parentheses. Since the first set of parentheses has a 9 in front, we are actually adding 36 to the left-hand side. Similarly, we are adding 36 to the second set as well. Therefore the equation becomes

$\begin{array}{}\\ 9\left({x}^{2}-4x+4\right)+4\left({y}^{2}+6y+9\right)=-36+36+36\hfill \\ 9\left({x}^{2}-4x+4\right)+4\left({y}^{2}+6y+9\right)=36.\hfill \end{array}$

Now factor both sets of parentheses and divide by 36:

$\begin{array}{}\\ \hfill 9{\left(x-2\right)}^{2}+4{\left(y+3\right)}^{2}& =\hfill & 36\hfill \\ \hfill \frac{9{\left(x-2\right)}^{2}}{36}+\frac{4{\left(y+3\right)}^{2}}{36}& =\hfill & 1\hfill \\ \hfill \frac{{\left(x-2\right)}^{2}}{4}+\frac{{\left(y+3\right)}^{2}}{9}& =\hfill & 1.\hfill \end{array}$

The equation is now in standard form. Comparing this to [link] gives $h=2,$ $k=-3,$ $a=3,$ and $b=2.$ This is a vertical ellipse with center at $\left(2,-3\right),$ major axis 6, and minor axis 4. The graph of this ellipse appears as follows.

Put the equation $9{x}^{2}+16{y}^{2}+18x-64y-71=0$ into standard form and graph the resulting ellipse.

$\frac{{\left(x+1\right)}^{2}}{16}+\frac{{\left(y-2\right)}^{2}}{9}=1$

According to Kepler’s first law of planetary motion, the orbit of a planet around the Sun is an ellipse with the Sun at one of the foci as shown in [link] (a). Because Earth’s orbit is an ellipse, the distance from the Sun varies throughout the year. A commonly held misconception is that Earth is closer to the Sun in the summer. In fact, in summer for the northern hemisphere, Earth is farther from the Sun than during winter. The difference in season is caused by the tilt of Earth’s axis in the orbital plane. Comets that orbit the Sun, such as Halley’s Comet, also have elliptical orbits, as do moons orbiting the planets and satellites orbiting Earth.

do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
Do somebody tell me a best nano engineering book for beginners?
what is fullerene does it is used to make bukky balls
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
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
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 ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
what's the easiest and fastest way to the synthesize AgNP?
China
Cied
types of nano material
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
what is nano technology
what is system testing?
preparation of nanomaterial
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
what is system testing
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
how did you get the value of 2000N.What calculations are needed to arrive at it
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