# 12.7 Ellipses: from definition to equation

 Page 1 / 1
A teacher's guide to the connection between the definition and equation of an ellipse, and how to get from one to the other.
 Here is the geometric definition of an ellipse. There are two points called the “foci”: in this case, (-3,0) and (3,0) . A point is on the ellipse if the sum of its distances to both foci is a certain constant: in this case, I’ll use 10 . Note that the foci define the ellipse, but are not part of it.

The point ( $x$ , $y$ ) represents any point on the ellipse. $d1$ is its distance from the first focus, and $d2$ to the second. So the ellipse is defined geometrically by the relationship: $d1+d2=10$ .

To calculate $d1$ and $d2$ , we use the Pythagorean Theorem as always: drop a straight line down from ( $x$ , $y$ ) to create the right triangles. Please verify this result for yourself! You should find that $d1=\sqrt{\left(x+3{\right)}^{2}+{y}^{2}}$ and $d2=\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}$ . So the equation becomes:

$\sqrt{\left(x+3{\right)}^{2}+{y}^{2}}+\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}=10$ . This defines our ellipse

The goal now is to simplify it. We did problems like this earlier in the year (radical equations, the “harder” variety that have two radicals). The way you do it is by isolating the square root, and then squaring both sides. In this case, there are two square roots, so we will need to go through that process twice.

 $\sqrt{\left(x+3{\right)}^{2}+{y}^{2}}=10–\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}$ Isolate a radical $\left(x+3{\right)}^{2}+{y}^{2}=100–20\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}+\left(x–3{\right)}^{2}+{y}^{2}$ Square both sides $\left({x}^{2}+6x+9\right)+{y}^{2}=100–20\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}+\left({x}^{2}–6x+9\right)+{y}^{2}$ Multiply out the squares $12x=100–20\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}$ Cancel&combine like terms $\sqrt{\left(x-3{\right)}^{2}+{y}^{2}}=5–\frac{3}{5}x$ Rearrange, divide by 20 $\left(x–3{\right)}^{2}+{y}^{2}=25–6x+\frac{9}{\text{25}}{x}^{2}$ Square both sides again $\left({x}^{2}–6x+9\right)+{y}^{2}=25–6x+\frac{9}{\text{25}}{x}^{2}$ Multiply out the square $\frac{\text{16}}{\text{25}}{x}^{2}+{y}^{2}=16$ Combine like terms $\frac{{x}^{2}}{\text{25}}+\frac{{y}^{2}}{\text{16}}=1$ Divide by 16

…and we’re done! Now, according to the “machinery” of ellipses, what should that equation look like? Horizontal or vertical? Where should the center be? What are $a$ , $b$ , and $c$ ? Does all that match the picture we started with?

anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
Introduction about quantum dots in nanotechnology
what does nano mean?
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?
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
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
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
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
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?
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.
Got questions? Join the online conversation and get instant answers!