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Hyperbolas also have interesting reflective properties. A ray directed toward one focus of a hyperbola is reflected by a hyperbolic mirror toward the other focus. This concept is illustrated in the following figure.

A hyperbola is drawn that is open to the right and left. There is a ray pointing to a point on the right hyperbola marked “Light from star.” It hits a “Mirror surface” and bounces to the focus on the other side of the hyperbola. There is dashed line from where the point hits the mirror surface to the focus on that side of the hyperbola.
A hyperbolic mirror used to collect light from distant stars.

This property of the hyperbola has important applications. It is used in radio direction finding (since the difference in signals from two towers is constant along hyperbolas), and in the construction of mirrors inside telescopes (to reflect light coming from the parabolic mirror to the eyepiece). Another interesting fact about hyperbolas is that for a comet entering the solar system, if the speed is great enough to escape the Sun’s gravitational pull, then the path that the comet takes as it passes through the solar system is hyperbolic.

Eccentricity and directrix

An alternative way to describe a conic section involves the directrices, the foci, and a new property called eccentricity. We will see that the value of the eccentricity of a conic section can uniquely define that conic.


The eccentricity     e of a conic section is defined to be the distance from any point on the conic section to its focus, divided by the perpendicular distance from that point to the nearest directrix. This value is constant for any conic section, and can define the conic section as well:

  1. If e = 1 , the conic is a parabola.
  2. If e < 1 , it is an ellipse.
  3. If e > 1 , it is a hyperbola.

The eccentricity of a circle is zero. The directrix of a conic section is the line that, together with the point known as the focus, serves to define a conic section. Hyperbolas and noncircular ellipses have two foci and two associated directrices. Parabolas have one focus and one directrix.

The three conic sections with their directrices appear in the following figure.

This figure has three figures. In the first is an ellipse, with center at the origin, foci at (c, 0) and (−c, 0), half of its vertical height being b, half of its horizontal length being a, and directrix x = ±a2/c. The second figure is a parabola with vertex at the origin, focus (a, 0), and directrix x = −a. The third figure is a hyperbola with center at the origin, foci at (c, 0) and (−c, 0), vertices at (a, 0) and (−a, 0), and directices at x = ±a2/c.
The three conic sections with their foci and directrices.

Recall from the definition of a parabola that the distance from any point on the parabola to the focus is equal to the distance from that same point to the directrix. Therefore, by definition, the eccentricity of a parabola must be 1. The equations of the directrices of a horizontal ellipse are x = ± a 2 c . The right vertex of the ellipse is located at ( a , 0 ) and the right focus is ( c , 0 ) . Therefore the distance from the vertex to the focus is a c and the distance from the vertex to the right directrix is a 2 c c . This gives the eccentricity as

e = a c a 2 c a = c ( a c ) a 2 a c = c ( a c ) a ( a c ) = c a .

Since c < a , this step proves that the eccentricity of an ellipse is less than 1. The directrices of a horizontal hyperbola are also located at x = ± a 2 c , and a similar calculation shows that the eccentricity of a hyperbola is also e = c a . However in this case we have c > a , so the eccentricity of a hyperbola is greater than 1.

Determining eccentricity of a conic section

Determine the eccentricity of the ellipse described by the equation

( x 3 ) 2 16 + ( y + 2 ) 2 25 = 1 .

From the equation we see that a = 5 and b = 4 . The value of c can be calculated using the equation a 2 = b 2 + c 2 for an ellipse. Substituting the values of a and b and solving for c gives c = 3 . Therefore the eccentricity of the ellipse is e = c a = 3 5 = 0.6 .

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Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
Nasa has use it in the 60's, copper as water purification in the moon travel.
nanocopper obvius
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
can you provide the details of the parametric equations for the lines that defince doubly-ruled surfeces (huperbolids of one sheet and hyperbolic paraboloid). Can you explain each of the variables in the equations?
Radek Reply

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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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