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[[Image:Excentricidad.svg|thumb|Point F is a focus point for the red ellipse, green parabola and blue hyperbola.]]
== Air Max 1 Nz  . ==
In [[geometry]], the '''foci''' ({{IPAc-en|ˈ|f|oʊ|s|aɪ}}; singular '''focus''') are a pair of special points with reference to which any of a variety of curves is constructed. For example, foci can be used in defining [[conic section]]s, the four types of which are the [[circle]], [[ellipse]], [[parabola]], and [[hyperbola]]. In addition, foci are used to define the [[Cassini oval]] and the [[Cartesian oval]].


==Conics in geometry==
55 Top [http://nikeairmax1nz.blog.co.nz/ Air Max 1 Nz] reasons to Mail an announcement<br><br>There are several factors to weigh when it comes to the necessity to send out an argument. As a publicist I have sent a huge number of releases over the years and even though there won't be any solid rules, the key factor is you should make sure it's newsworthy and necessary to your reader. Anything else and just a waste for your people in the media.<br><br>A good news release can accomplish many items too. Countless uses for flash to announce information on the public, your investors, the media, your customers and in many cases your competitors about you as well as your activities. That can help my clients determine if something is newsworthy I compiled a directory of fifty five news release ideas I have for those to obtain their ideas flowing concerning their own businesses. Many are for general consumer media and several might not affect all business types.<br><br>Once you get the production written what to do now? How would you stick it to the media? Just how can a firm or individual know if it may possibly handle media relations themselves or maybe if it must hire a pr firm, an unbiased publicist or even a full fledged marketing firm? If you aren't completely certain after debating the pros and cons, ask these questions:<br><br>+ Shall we be held getting each of the PR we deserve?<br><br>+ Is our competition getting than their share of media coverage?<br><br>+ Would attention bring more business to your firm?<br><br>+ Ought to use a PR technique of continuous year long attention?<br><br>+ Is our in-house "PR person or department" overburdened with "in house" work just like the company newsletter?<br><br>For starters, let's define a PR firm. A lot of people interchange a PR firm [http://ralphlaurenuk.mycylex.co.uk/ Ralph Lauren Uk] using a marketing firm, or marketing agency, as well as ad agency. Basically an open relations firm handles media relations and is particularly the interface from your company plus the press. A superb pitch about a story [http://airjordanshoesuk.mycylex.co.uk/ Air Jordan Shoes Uk] that may interest individuals who read, watch or tune in to a selected media outlet gets coverage.<br><br>Many larger companies rely upon in house staff [http://raybanwayfarernz0.blog.co.nz/ Ray Ban Aviators Nz] been trained in pr or marketing while some hire PR consultants or publicists to deal with their PR campaigns. Paradoxically, the busier you have, the greater it really is to parlay, or "set aside" consistent, important PR activities. Do not get caught because trap!<br><br>"Public Relations is a craft that will require PASSION," says Nicassio. "You may require PR, and you will probably have folks to conduct your page rank, marketing, advertising campaigns but that is insufficient. His clients are actually featured by Hello America, FOX Friends, CNN, ABC Nightly News, The newest York Times, Nightline, TIME, PBS, NPR, the Los Angeles Times, USA Today, Washington Post, Family Circle, Woman's World, Howard Stern among others.<br><br>Other sorts of articles by Scott LorenzUsing Book Signings to promote Your Book<br><br>To be a book publicist I've a strong opinion about book tours.<br><br>A message Is Priceless, Any time To shield It truly is Before it's Damaged.<br><br>Does your legal strategy include media relations? Or even consider this.<br><br>Over the Ronald Regan Presidency, Former Secretary from the . .<br><br>Google Book Search Is fantastic Book Marketing and Book Promotion<br><br>The jury is in as well as it a split decision. Split about the Google Book Search Program that is. A lot of people enjoy it. Others think it's the apocalypse. I absolutely shouldn't wind up in the legal ramifications, .<ul>
 
 
===Defining conics in terms of two foci===
  <li>[http://enseignement-lsf.com/spip.php?article64#forum18412995 http://enseignement-lsf.com/spip.php?article64#forum18412995]</li>
 
 
An ellipse can be defined as the [[Locus (mathematics)|locus]] of points for each of which the sum of the distances to two given foci is a constant.
  <li>[http://bbs.hbqcw9.com/forum.php?mod=viewthread&tid=1425156 http://bbs.hbqcw9.com/forum.php?mod=viewthread&tid=1425156]</li>
 
 
A circle is the special case of an ellipse in which the two foci coincide with each other. Thus, a circle can be more simply defined as the locus of points each of which is a fixed distance from a single given focus.  A circle can also be defined as the [[Circles of Apollonius|circle of Apollonius]], in terms of two different foci, as the set of points having a fixed ratio of distances to the two foci.
  <li>[http://www.songshumi.com/thread-24417-1-1.html http://www.songshumi.com/thread-24417-1-1.html]</li>
 
 
A parabola is a limiting case of an ellipse in which one of the foci is a [[point at infinity]].
  <li>[http://neijiang.tyfo.com/news/html/?70473.html http://neijiang.tyfo.com/news/html/?70473.html]</li>
 
 
A hyperbola can be defined as the locus of points for each of which the absolute value of the difference between the distances to two given foci is a constant.
  <li>[http://www.tianwaitianrihua.com/news/html/?708340.html http://www.tianwaitianrihua.com/news/html/?708340.html]</li>
 
 
===Defining conics in terms of a focus and a directrix===
</ul>
 
It is also possible to describe all the conic sections in terms of a single focus and a single [[Conic section#Eccentricity, focus and directrix|directrix]], which is a given line not containing the focus. A conic is defined as the locus of points for each of which the distance to the focus divided by the distance to the directrix is a fixed positive constant, called the eccentricity ''e''. If ''e'' is between zero and one the conic is an ellipse; if ''e''=1 the conic is a parabola; and if ''e''>1 the conic is a hyperbola. If the distance to the focus is fixed and the directrix is a [[line at infinity]], so the eccentricity is zero, then the conic is a circle.
 
===Defining conics in terms of a focus and a directrix circle===
 
It is also possible to describe all the conic sections as loci of points that are equidistant from a single focus and a single, circular directrix. For the ellipse, both the focus and the center of the directrix circle have finite coordinates and the radius of the directrix circle is greater than the distance between the center of this circle and the focus; thus, the focus is inside the directrix circle. The ellipse thus generated has its second focus at the center of the directrix circle, and the ellipse lies entirely within the circle.
 
For the parabola, the center of the directrix moves to the point at infinity (see [[projective geometry]]). The directrix 'circle' becomes a curve with zero curvature, indistinguishable from a straight line. The two arms of the parabola become increasingly parallel as they extend, and 'at infinity' become parallel; using the principles of projective geometry, the two parallels intersect at the point at infinity and the parabola becomes a closed curve (elliptical projection).  
 
To generate a hyperbola, the radius of the directrix circle is chosen to be less than the distance between the center of this circle and the focus; thus, the focus is outside the directrix circle. The arms of the hyperbola approach asymptotic lines and the 'right-hand' arm of one branch of a hyperbola meets the 'left-hand' arm of the other branch of a hyperbola at the point at infinity; this is based on the principle that, in projective geometry, a single line meets itself at a point at infinity. The two branches of a hyperbola are thus the two (twisted) halves of a curve closed over infinity.  
 
In projective geometry, all conics are equivalent in the sense that every theorem that can be stated for one can be stated for the others.
 
===Astronomical significance===
In the [[gravitation]]al [[two-body problem]], the orbits of the two bodies are described by two overlapping conic sections each with one of their foci being coincident at the [[center of mass]] ([[Barycentric coordinates (astronomy)|barycenter]]).
 
==Cartesian and Cassini ovals==
 
A [[Cartesian oval]] is the set of points for each of which the [[weighted sum]] of the distances to two given foci is a constant. If the weights are equal, the special case of an ellipse results.
 
A [[Cassini oval]] is the set of points for each of which the product of the distances to two given foci is a constant.
 
==Generalization==
The concept of a focus can be generalized to arbitrary algebraic curves. Let ''C'' be a curve of class ''m'' and let ''I'' and ''J'' denote the [[circular points at infinity]]. Draw the ''m'' tangents to ''C'' through each of ''I'' and ''J''. There are two sets of ''m'' lines which will have ''m''<sup>2</sup> points of intersection, with exceptions in some cases due to singularities, etc. These points of intersection are the defined to be the foci of ''C''. In other words, a point ''P'' is a focus if both ''PI'' and ''PJ'' are tangent to ''C''. When ''C'' is a real curve, only the intersections of conjugate pairs are real, so there are ''m'' in a real foci and ''m''<sup>2</sup>−''m'' imaginary foci. When ''C'' is a conic, the real foci defined this way are exactly the foci which can be used in the geometric construction of ''C''.
 
==Confocal curves==
Let ''P''<sub>1</sub>, ''P''<sub>2</sub>, …, ''P<sub>m</sub>'' be given as foci of a curve ''C'' of class ''m''. Let ''P'' be the product of the tangential equations of these points and ''Q'' the product of the tangential equations of the circular points at infinity. Then all the lines which are common tangents to both ''P''=0 and ''Q''=0 are tangent to ''C''. So, by the [[AF+BG theorem]], the tangential equation of ''C'' has the form ''HP''+''KQ''=0. Since ''C'' has class ''m'', ''H'' must be a constant and ''K'' but have degree less than or equal to ''m''−2. The case ''H''=0 can be eliminated as degenerate, so the tangential equation of ''C'' can be written as ''P''+''fQ''=0 where ''f'' is an arbitrary polynomial of degree ''m''−2.<ref>Follows Hilton p. 69 with an appeal to AF+BG for simplification.</ref>
 
For example, let ''P''<sub>1</sub>=(1,0), ''P''<sub>2</sub>=(−1,0). The tangential equations are ''X''+1=0 and ''X''−1=0 so ''P''= ''X''<sup>2</sup>-1=0. The tangential equations for the circular points at infinity are ''X''+''iY''=0 and ''X''−''iY''=0 so ''Q''=''X''<sup>2</sup>+''Y''<sup>2</sup>. Therefore the tangential equation for a conic with the given foci is ''X''<sup>2</sup>-1+''c''(''X''<sup>2</sup>+''Y''<sup>2</sup>)=0, or (1+''c'')''X''<sup>2</sup>+''cY''<sup>2</sup>=1 where ''c'' is an arbitrary constant. In point coordinates this becomes
:<math>\frac{x^2}{1+c}+\frac{y^2}{c}=1.</math>
 
==References==
{{reflist}}
*{{cite book |title=Plane Algebraic Curves|first=Harold|last=Hilton|publisher=Oxford|year=1920|page=69
|url=http://www.archive.org/details/cu31924001544216}}
 
[[Category:Conic sections]]
[[Category:Geometric centers]]

Latest revision as of 12:54, 25 April 2014

Air Max 1 Nz .

55 Top Air Max 1 Nz reasons to Mail an announcement

There are several factors to weigh when it comes to the necessity to send out an argument. As a publicist I have sent a huge number of releases over the years and even though there won't be any solid rules, the key factor is you should make sure it's newsworthy and necessary to your reader. Anything else and just a waste for your people in the media.

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Once you get the production written what to do now? How would you stick it to the media? Just how can a firm or individual know if it may possibly handle media relations themselves or maybe if it must hire a pr firm, an unbiased publicist or even a full fledged marketing firm? If you aren't completely certain after debating the pros and cons, ask these questions:

+ Shall we be held getting each of the PR we deserve?

+ Is our competition getting than their share of media coverage?

+ Would attention bring more business to your firm?

+ Ought to use a PR technique of continuous year long attention?

+ Is our in-house "PR person or department" overburdened with "in house" work just like the company newsletter?

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Does your legal strategy include media relations? Or even consider this.

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