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Conic Sections ©Mathworld

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**Conic Sections - Definition**

A conic section is a curve formed by intersecting cone with a plane There are four types of Conic sections

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**Conic Sections - Four Types**

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Parabolas © Art Mayoff © Long Island Fountain Company

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What’s in a Parabola A parabola is the set of all points in a plane such that each point in the set is equidistant from a line called the directrix and a fixed point called the focus. (x, y) Copyright © , Math Academy Online™ / Platonic Realms™.

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**Why is the focus so important?**

© Jill Britton, September 25, 2003

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The Parabola One of nature's best known approximations to parabolas is the path taken by a body projected upward and obliquely to the pull of gravity, as in the parabolic trajectory of a golf ball. The friction of air and the pull of gravity will change slightly the projectile's path from that of a true parabola, but in many cases the error is insignificant.

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The Parabola This discovery by Galileo in the 17th century made it possible for cannoneers to work out the kind of path a cannonball would travel if it were hurtled through the air at a specific angle.

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The Parabola When a baseball is hit into the air, it follows a parabolic path; the center of gravity of a leaping porpoise describes a parabola.

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The Parabola The easiest way to visualize the path of a projectile is to observe a waterspout. Each molecule of water follows the same path and, therefore, reveals a picture of the curve. The fountains of the Bellagio Hotel in Las Vegas comprise a parabolic chorus line.

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The Parabola Parabolas exhibit unusual and useful reflective properties. If a light is placed at the focus of a parabolic mirror (a curved surface formed by rotating a parabola about its axis), the light will be reflected in rays parallel to said axis. In this way a straight beam of light is formed. It is for this reason that parabolic surfaces are used for headlamp reflectors. The bulb is placed at the focus for the high beam and a little above the focus for the low beam.

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The Parabola The opposite principle is used in the giant mirrors in reflecting telescopes and in antennas used to collect light and radio waves from outer space: the beam comes toward the parabolic surface and is brought into focus at the focal point. The instrument with the largest single-piece parabolic mirror is the Subaru telescope at the summit of Mauna Kea in Hawaii (effective diameter: 8.2 m).

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The Parabola Heat waves, as well as light and sound waves, are reflected to the focal point of a parabolic surface. If a parabolic reflector is turned toward the sun, flammable material placed at the focus may ignite. A solar furnace produces heat by focusing sunlight by means of a parabolic mirror arrangement. Light is sent to it by set of moveable mirrors computerized to follow the sun during the day. Solar cooking involves a similar use of a parabolic mirror.

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Parabola The Standard Form of a Parabola that opens to the right and has a vertex at (0,0) is…… ©1999 Addison Wesley Longman, Inc.

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Parabola The Parabola that opens to the right and has a vertex at (0,0) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (p,0) This makes the equation of the directrix x = -p The makes the axis of symmetry the x-axis (y = 0)

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Parabola The Standard Form of a Parabola that opens to the left and has a vertex at (0,0) is…… © Shelly Walsh

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Parabola The Parabola that opens to the left and has a vertex at (0,0) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus(-p,0) This makes the equation of the directrix x = p The makes the axis of symmetry the x-axis (y = 0)

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Parabola The Standard Form of a Parabola that opens up and has a vertex at (0,0) is…… © SparkNotes LLC, All Rights Reserved

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Parabola The Parabola that opens up and has a vertex at (0,0) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (0,p) This makes the equation of the directrix y = -p This makes the axis of symmetry the y-axis (x = 0)

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Parabola The Standard Form of a Parabola that opens down and has a vertex at (0,0) is…… ©1999 Addison Wesley Longman, Inc.

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Parabola The Parabola that opens down and has a vertex at (0,0) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (0,-p) This makes the equation of the directrix y = p This makes the axis of symmetry the y-axis (x = 0)

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Parabola The Standard Form of a Parabola that opens to the right and has a vertex at (h,k) is…… © Shelly Walsh

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Parabola The Parabola that opens to the right and has a vertex at (h,k) has the following characteristics…….. p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (h+p, k) This makes the equation of the directrix x = h – p This makes the axis of symmetry

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Parabola The Standard Form of a Parabola that opens to the left and has a vertex at (h,k) is…… ©June Jones, University of Georgia

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Parabola The Parabola that opens to the left and has a vertex at (h,k) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (h – p, k) This makes the equation of the directrix x = h + p The makes the axis of symmetry

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Parabola The Standard Form of a Parabola that opens up and has a vertex at (h,k) is…… Copyright © Oswego City School District Regents Exam Prep Center

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Parabola The Parabola that opens up and has a vertex at (h,k) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (h , k + p) This makes the equation of the directrix y = k – p The makes the axis of symmetry

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Parabola The Standard Form of a Parabola that opens down and has a vertex at (h,k) is…… Copyright © Oswego City School District Regents Exam Prep Center

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Parabola The Parabola that opens down and has a vertex at (h,k) has the following characteristics…… p is the distance from the vertex of the parabola to the focus or directrix This makes the coordinates of the focus (h , k - p) This makes the equation of the directrix y = k + p This makes the axis of symmetry

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**Ellipse © Jill Britton, September 25, 2003**

Statuary Hall in the U.S. Capital building is elliptic. It was in this room that John Quincy Adams, while a member of the House of Representatives, discovered this acoustical phenomenon. He situated his desk at a focal point of the elliptical ceiling, easily eavesdropping on the private conversations of other House members located near the other focal point.

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What is in an Ellipse? The set of all points in the plane, the sum of whose distances from two fixed points, called the foci, is a constant. (“Foci” is the plural of “focus”, and is pronounced FOH-sigh.) Copyright © , Math Academy Online™ / Platonic Realms™.

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**Why are the foci of the ellipse important?**

The ellipse has an important property that is used in the reflection of light and sound waves. Any light or signal that starts at one focus will be reflected to the other focus. This principle is used in lithotripsy, a medical procedure for treating kidney stones. The patient is placed in a elliptical tank of water, with the kidney stone at one focus. High-energy shock waves generated at the other focus are concentrated on the stone, pulverizing it.

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**Why are the foci of the ellipse important?**

St. Paul's Cathedral in London. If a person whispers near one focus, he can be heard at the other focus, although he cannot be heard at many places in between. © Kevin Matthews and Artifice, Inc. All Rights Reserved.

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The Ellipse Though not so simple as the circle, the ellipse is nevertheless the curve most often "seen" in everyday life. The reason is that every circle, viewed obliquely, appears elliptical.

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The Ellipse Any cylinder sliced on an angle will reveal an ellipse in cross-section (as seen in the Tycho Brahe Planetarium in Copenhagen).

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The Ellipse Tilt a glass of water and the surface of the liquid acquires an elliptical outline. Salami is often cut obliquely to obtain elliptical slices which are larger.

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The Ellipse The early Greek astronomers thought that the planets moved in circular orbits about an unmoving earth, since the circle is the simplest mathematical curve. In the 17th century, Johannes Kepler eventually discovered that each planet travels around the sun in an elliptical orbit with the sun at one of its foci.

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The Ellipse

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**The Ellipse Click here to see the orbit**

The orbits of the moon and of artificial satellites of the earth are also elliptical as are the paths of comets in permanent orbit around the sun. Halley's Comet takes about 76 years to travel abound our sun. Edmund Halley saw the comet in 1682 and correctly predicted its return in Although he did not live long enough to see his prediction come true, the comet is named in his honor. Click here to see the orbit

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The Ellipse On a far smaller scale, the electrons of an atom move in an approximately elliptical orbit with the nucleus at one focus.

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The Ellipse The ellipse has an important property that is used in the reflection of light and sound waves. Any light or signal that starts at one focus will be reflected to the other focus. This principle is used in lithotripsy, a medical procedure for treating kidney stones. The patient is placed in a elliptical tank of water, with the kidney stone at one focus. High-energy shock waves generated at the other focus are concentrated on the stone, pulverizing it.

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The Ellipse The principle is also used in the construction of "whispering galleries" such as in St. Paul's Cathedral in London. If a person whispers near one focus, he can be heard at the other focus, although he cannot be heard at many places in between.

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The Ellipse Statuary Hall in the U.S. Capital building is elliptic. It was in this room that John Quincy Adams, discovered this acoustical phenomenon. He situated his desk at a focal point of the elliptical ceiling, easily eaves-dropping on the private conversations of other House members located near the other focal point.

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The Ellipse The ability of the ellipse to rebound an object starting from one focus to the other focus can be demonstrated with an elliptical billiard table. When a ball is placed at one focus and is thrust with a cue stick, it will rebound to the other focus. If the billiard table is live enough, the ball will continue passing through each focus and rebound to the other.

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**Ellipse General Rules x and y are both squared**

Equation always equals(=) 1 Equation is always plus(+) a2 is always the biggest denominator c2 = a2 – b2 c is the distance from the center to each foci on the major axis The center is in the middle of the 2 vertices, the 2 covertices, and the 2 foci.

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Ellipse General Rules a is the distance from the center to each vertex on the major axis b is the distance from the center to each vertex on the minor axis (co-vertices) Major axis has a length of 2a Minor axis has a length of 2b Eccentricity(e): e = c/a (The closer e gets to 0, the closer it is to being circular)

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Ellipse The standard form of the ellipse with a center at (0,0) and a horizontal axis is……

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Ellipse The ellipse with a center at (0,0) and a horizontal axis has the following characteristics…… Vertices ( a,0) Co-Vertices (0, b) Foci ( c,0) © Cabalbag, Porter, Chadwick, and Liefting

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Ellipse The standard form of the ellipse with a center at (0,0) and a vertical axis is……

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Ellipse The ellipse with a center at (0,0) and a vertical axis has the following characteristics…… Vertices (0, a) Co-Vertices ( b,0) Foci (0, c) © Cabalbag, Porter, Chadwick, and Liefting

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Ellipse The standard form of the ellipse with a center at (h,k) and a horizontal axis is……

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Ellipse The ellipse with a center at (h,k) and a horizontal axis has the following characteristics…… Vertices (h a , k) Co-Vertices (h, k b) Foci (h c , k) ©Sellers, James

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Ellipse The standard form of the ellipse with a center at (h,k) and a vertical axis is……

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Ellipse The ellipse with a center at (h,k) and a vertical axis has the following characteristics…… Vertices (h, k a) Co-Vertices (h b , k) Foci (h, k c) © Joan Bookbinder

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**Hyperbola © Jill Britton, September 25, 2003**

The huge chimney of a nuclear power plant has the shape of a hyperboloid, as does the architecture of the James S. McDonnell Planetarium of the St. Louis Science Center.

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What is a Hyperbola? The set of all points in the plane, the difference of whose distances from two fixed points, called the foci, remains constant. Copyright © , Math Academy Online™ / Platonic Realms™.

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**Where are the Hyperbolas?**

A sonic boom shock wave has the shape of a cone, and it intersects the ground in part of a hyperbola. It hits every point on this curve at the same time, so that people in different places along the curve on the ground hear it at the same time. Because the airplane is moving forward, the hyperbolic curve moves forward and eventually the boom can be heard by everyone in its path. © Jill Britton, September 25, 2003

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The Hyperbola If a right circular cone is intersected by a plane parallel to its axis, part of a hyperbola is formed. Such an intersection can occur in physical situations as simple as sharpening a pencil that has a polygonal cross section or in the patterns formed on a wall by a lamp shade.

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The Hyperbola A sonic boom shock wave has the shape of a cone, and it intersects the ground in part of a hyperbola. It hits every point on this curve at the same time, so that people in different places along the curve on the ground hear it at the same time. Because the airplane is moving forward, the hyperbolic curve moves forward and eventually the boom can be heard by everyone in its path.

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The Hyperbola A hyperbola revolving around its axis forms a surface called a hyperboloid. The cooling tower of a steam power plant has the shape of a hyperboloid, as does the architecture of the James S. McDonnell Planetarium of the St. Louis Science Center.

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The Hyperbola All three conic sections can be characterized by moiré patterns. If the center of each of two sets of concentric circles is the source of a radio signal, the synchronized signals would intersect one another in associated hyperbolas. This principle forms the basis of a hyperbolic radio navigation system known as Loran (Long Range Navigation).

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**Hyperbola General Rules x and y are both squared**

Equation always equals(=) 1 Equation is always minus(-) a2 is always the first denominator c2 = a2 + b2 c is the distance from the center to each foci on the major axis a is the distance from the center to each vertex on the major axis

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**Hyperbola General Rules**

b is the distance from the center to each midpoint of the rectangle used to draw the asymptotes. This distance runs perpendicular to the distance (a). Major axis has a length of 2a Eccentricity(e): e = c/a (The closer e gets to 1, the closer it is to being circular If x2 is first then the hyperbola is horizontal If y2 is first then the hyperbola is vertical.

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**Hyperbola General Rules**

The center is in the middle of the 2 vertices and the 2 foci. The vertices and the covertices are used to draw the rectangles that form the asymptotes. The vertices and the covertices are the midpoints of the rectangle The covertices are not labeled on the hyperbola because they are not actually part of the graph

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Hyperbola The standard form of the Hyperbola with a center at (0,0) and a horizontal axis is……

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Hyperbola The Hyperbola with a center at (0,0) and a horizontal axis has the following characteristics…… Vertices ( a,0) Foci ( c,0) Asymptotes:

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Hyperbola The standard form of the Hyperbola with a center at (0,0) and a vertical axis is……

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Hyperbola The Hyperbola with a center at (0,0) and a vertical axis has the following characteristics…… Vertices (0, a) Foci ( 0, c) Asymptotes:

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Hyperbola The standard form of the Hyperbola with a center at (h,k) and a horizontal axis is……

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Hyperbola The Hyperbola with a center at (h,k) and a horizontal axis has the following characteristics…… Vertices (h a, k) Foci (h c, k ) Asymptotes:

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Hyperbola The standard form of the Hyperbola with a center at (h,k) and a vertical axis is……

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Hyperbola The Hyperbola with a center at (h,k) and a vertical axis has the following characteristics…… Vertices (h, k a) Foci (h, k c) Asymptotes: ©Sellers, James

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**Rotating the Coordinate Axis**

© James Wilson

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**Equations for Rotating the Coordinate Axes**

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Resources Bookbinder, John. Unit 8: Conic Sections (College Algebra Online). 2000. June 3, 2004 <http://www.distancemath.com/unit8/ch8p1.htm>. Britton, Jill. Occurrence of the Conics. September 25, 2003. June 3, 2004 <http://ccins.camosun.bc.ca/~jbritton/jbconics.htm>. Cabalbag, Christain, and Porter, Amanda and Chadwick, Justin and Liefting. Nick. Graphing Conic Sections (Microsoft Power Point Presentation 1997). June3, 2004 <http://www.granite.k12.ut.us/Hunter_High/StaffPages/Olsen_P/ClassWebSite/2003%20student%20projects/27circlesandelipse.ppt

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Resources Finney, Ross, et. al. Calculus: Graphical, Numerical, Algebraic. Scott Foresman-Addison Wesley, 1999. Jones, June. Instructional Unit on Conic Sections. University of Georgia. June 3, 2004 Mathews, Kevin. Great Buildings Online. Great Buildings. une 3, 2004 <http://www.GreatBuildings.com/buildings/Saint_Pauls_Cathedral.html

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**Resources Mueller, William. Modeling Periodicity . **

Mayoff, Art. San Francisco and the Golden Gate Bridge. June 3, 2004 Mueller, William. Modeling Periodicity . <http://www.wmueller.com/precalculus/funcdata/1_10.html>. PRIME Articles. Platomic Realms. <http://www.mathacademy.com/pr/prime/index.asp>.

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Resources Quadratics. Spark Notes from Barnes and Noble. June 3, 2004 <http://www.sparknotes.com/math/algebra1/quadratics/section1.html Roberts, Donna. Mathematics A . Oswego City School District Regents Exam Prep. June, 3, 2004 <http://regentsprep.org/Regents/math/math-topic.cfm?TopicCode=conics>. Seek One Web Services, Long Island Fountain Company. <http://www.lifountain.com/fountainideas.html>. Sellers, James, Introduction to Conics, June 8, 2004.

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**Resources Walsh, Shelly. Chapter 9 (Precalculus). June 3, 2004 **

Walsh, Shelly. Chapter 9 (Precalculus). June 3, 2004 Weissteing, Eric W. "Conic Section." From MathWorld--A Wolfram Web Resource. Wilson, James W. CURVE BUILDING. An Exploration with Algebraic Relations University of Georgia. June 3, 2004

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**Other Works Cited Jill Britton Online Encyclopedia**

Online Encyclopedia Wikipedia The Comet’s Tale: Orbits

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Circle ©National Science Foundation

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Circle The Standard Form of a circle with a center at (0,0) and a radius, r, is…….. center (0,0) radius = 2 Copyright © Oswego City School District Regents Exam Prep Center

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Circles The Standard Form of a circle with a center at (h,k) and a radius, r, is…….. center (3,3) radius = 2 Copyright © Oswego City School District Regents Exam Prep Center

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