In
mathematicsMathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
, the
parabola (icon; plural
parabolae or
parabolas, from the
GreekGreek is an independent branch of the IndoEuropean family of languages. Native to the southern Balkans, it has the longest documented history of any IndoEuropean language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
παραβολή) is a
conic sectionIn mathematics, a conic section is a curve obtained by intersecting a cone with a plane. In analytic geometry, a conic may be defined as a plane algebraic curve of degree 2...
, the intersection of a right circular
conical surfaceIn geometry, a conical surface is the unbounded surface formed by the union of all the straight lines that pass through a fixed point — the apex or vertex — and any point of some fixed space curve — the directrix — that does not contain the apex...
and a
planeIn mathematics, a plane is a flat, twodimensional surface. A plane is the two dimensional analogue of a point , a line and a space...
parallel to a generating straight line of that surface. Given a point (the
focusIn geometry, the foci 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 sections, the four types of which are the circle, ellipse, parabola, and hyperbola...
) and a corresponding line (the
directrix) on the plane, the
locusIn geometry, a locus is a collection of points which share a property. For example a circle may be defined as the locus of points in a plane at a fixed distance from a given point....
of
pointIn geometry, topology and related branches of mathematics a spatial point is a primitive notion upon which other concepts may be defined. In geometry, points are zerodimensional; i.e., they do not have volume, area, length, or any other higherdimensional analogue. In branches of mathematics...
s in that plane that are
equidistantDistance is a numerical description of how far apart objects are. In physics or everyday discussion, distance may refer to a physical length, or an estimation based on other criteria . In mathematics, a distance function or metric is a generalization of the concept of physical distance...
from them is a parabola.
The line perpendicular to the directrix and passing through the focus (that is, the line that splits the parabola through the middle) is called the "axis of symmetry". The point on the axis of symmetry that intersects the parabola is called the "
vertexIn the geometry of curves, a vertex is a point of where the first derivative of curvature is zero. This is typically a local maximum or minimum of curvature. Other special cases may occur, for instance when the second derivative is also zero, or when the curvature is constant...
", and it is the point where the
curvatureIn mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...
is greatest. Parabolas can open up, down, left, right, or in some other arbitrary direction. Any parabola can be repositioned and rescaled to fit exactly on any other parabola — that is, all parabolas are
similarTwo geometrical objects are called similar if they both have the same shape. More precisely, either one is congruent to the result of a uniform scaling of the other...
.
The parabola has many important applications, from automobile headlight reflectors to the design of ballistic missiles. They are frequently used in
physicsPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
,
engineeringEngineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
, and many other areas.
History
The earliest known work on conic sections was by
MenaechmusMenaechmus was an ancient Greek mathematician and geometer born in Alopeconnesus in the Thracian Chersonese, who was known for his friendship with the renowned philosopher Plato and for his apparent discovery of conic sections and his solution to the thenlongstanding problem of doubling the cube...
in the fourth century BC. He discovered a way to solve the problem of
doubling the cubeDoubling the cube is one of the three most famous geometric problems unsolvable by compass and straightedge construction...
using parabolae. (The solution, however, does not meet the requirements imposed by compass and straightedge construction.) The area enclosed by a parabola and a line segment, the socalled "parabola segment", was computed by
ArchimedesArchimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...
via the
method of exhaustionThe method of exhaustion is a method of finding the area of a shape by inscribing inside it a sequence of polygons whose areas converge to the area of the containing shape. If the sequence is correctly constructed, the difference in area between the nth polygon and the containing shape will...
in the third century BC, in his
The Quadrature of the ParabolaThe Quadrature of the Parabola is a treatise on geometry, written by Archimedes in the 3rd century BC. Written as a letter to his friend Dositheus, the work presents 24 propositions regarding parabolas, culminating in a proof that the area of a parabolic segment is 4/3 that of a certain inscribed...
. The name "parabola" is due to
ApolloniusApollonius of Perga [Pergaeus] was a Greek geometer and astronomer noted for his writings on conic sections. His innovative methodology and terminology, especially in the field of conics, influenced many later scholars including Ptolemy, Francesco Maurolico, Isaac Newton, and René Descartes...
, who discovered many properties of conic sections. The focus–directrix property of the parabola and other conics is due to
PappusPappus of Alexandria was one of the last great Greek mathematicians of Antiquity, known for his Synagoge or Collection , and for Pappus's Theorem in projective geometry...
.
GalileoGalileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...
showed that the path of a projectile follows a parabola, a consequence of uniform acceleration due to gravity.
The idea that a
parabolic reflectorA parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
could produce an image was already well known before the invention of the
reflecting telescopeA reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
. Designs were proposed in the early to mid seventeenth century by many
mathematicianA mathematician is a person whose primary area of study is the field of mathematics. Mathematicians are concerned with quantity, structure, space, and change....
s including
René DescartesRené Descartes ; was a French philosopher and writer who spent most of his adult life in the Dutch Republic. He has been dubbed the 'Father of Modern Philosophy', and much subsequent Western philosophy is a response to his writings, which are studied closely to this day...
,
Marin MersenneMarin Mersenne, Marin Mersennus or le Père Mersenne was a French theologian, philosopher, mathematician and music theorist, often referred to as the "father of acoustics"...
, and James Gregory. When
Isaac NewtonSir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...
built the
first reflecting telescopeThe first reflecting telescope built by Sir Isaac Newton in 1668 is a landmark in the history of telescopes, being the first known successful reflecting telescope. It was the prototype for a design that later came to be called a newtonian telescope....
in 1668 he skipped using a parabolic mirror because of the difficulty of fabrication, opting for a spherical mirror. Parabolic mirrors are used in most modern reflecting telescopes and in satellite dishes and radar receivers.
Equation in Cartesian coordinates
Let the directrix be the line
x = −
p and let the focus be the point (
p, 0). If (
x,
y) is a point on the parabola then, by Pappus' definition of a parabola, it is the same distance from the directrix as the focus; in other words:
Squaring both sides and simplifying produces
as the equation of the parabola. By interchanging the roles of
x and
y one obtains the corresponding equation of a parabola with a vertical axis as
The equation can be generalized to allow the vertex to be at a point other than the origin by defining the vertex as the point (
h,
k). The equation of a parabola with a vertical axis then becomes
The last equation can be rewritten
so the graph of any function which is a polynomial of degree 2 in
x is a parabola with a vertical axis.
More generally, a parabola is a curve in the Cartesian plane defined by an
irreducibleIn mathematics, the adjective irreducible means that an object cannot be expressed as the product of two or more nontrivial factors in a given set. See also factorization....
equation — one that does not factor as a product of two not necessarily distinct linear equations — of the general conic form
with the parabola restriction that
where all of the coefficients are real and where
A and
C are not both zero. The equation is irreducible if and only if the determinant of the 3×3 matrix
is nonzero: that is, if (
AC 
B^{2}/4)
F +
BED/4 
CD^{2}/4 
AE^{2}/4 ≠ 0. The reducible case, also called the degenerate case, gives a pair of parallel lines, possibly real, possibly imaginary, and possibly coinciding with each other.
Other geometric definitions
A parabola may also be characterized as a conic section with an
eccentricityIn mathematics, the eccentricity, denoted e or \varepsilon, is a parameter associated with every conic section. It can be thought of as a measure of how much the conic section deviates from being circular.In particular,...
of 1. As a consequence of this, all parabolae are
similarTwo geometrical objects are called similar if they both have the same shape. More precisely, either one is congruent to the result of a uniform scaling of the other...
, meaning that while they can be different sizes, they are all the same shape. A parabola can also be obtained as the
limitIn mathematics, the limit of a function is a fundamental concept in calculus and analysis concerning the behavior of that function near a particular input....
of a sequence of
ellipseIn geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
s where one focus is kept fixed as the other is allowed to move arbitrarily far away in one direction. In this sense, a parabola may be considered an ellipse that has one focus at
infinityIn mathematics, the affinely extended real number system is obtained from the real number system R by adding two elements: +∞ and −∞ . The projective extended real number system adds a single object, ∞ and makes no distinction between "positive" or "negative" infinity...
. The parabola is an inverse transform of a
cardioidA cardioid is a plane curve traced by a point on the perimeter of a circle that is rolling around a fixed circle of the same radius. It is therefore a type of limaçon and can also be defined as an epicycloid having a single cusp...
.
A parabola has a single axis of reflective
symmetrySymmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...
, which passes through its focus and is perpendicular to its directrix. The point of intersection of this axis and the parabola is called the vertex. A parabola spun about this axis in three dimensions traces out a shape known as a
paraboloidIn mathematics, a paraboloid is a quadric surface of special kind. There are two kinds of paraboloids: elliptic and hyperbolic. The elliptic paraboloid is shaped like an oval cup and can have a maximum or minimum point....
of revolution.
The parabola is found in numerous situations in the physical world (see below).
Vertical axis of symmetry
where
.
Parametric form:
Horizontal axis of symmetry
where
.
Parametric form:
General parabola
The general form for a parabola is
This result is derived from the general conic equation given below:
and the fact that, for a parabola,
.
The equation for a general parabola with a focus point
F(
u,
v), and a directrix in the form
is
Latus rectum, semilatus rectum, and polar coordinates
In polar coordinates, a parabola with the focus at the origin and the directrix parallel to the
yaxis, is given by the equation

where
l is the
semilatus rectum: the distance from the focus to the parabola itself, measured along a line perpendicular to the axis. Note that this is twice the distance from the focus to the vertex of the parabola or the perpendicular distance from the focus to the latus rectum.
The latus rectum is the chord that passes through the focus and is perpendicular to the axis. It has a length of 2l.
Gaussmapped form
A
GaussmappedIn differential geometry, the Gauss map maps a surface in Euclidean space R3 to the unit sphere S2. Namely, given a surface X lying in R3, the Gauss map is a continuous map N: X → S2 such that N is a unit vector orthogonal to X at p, namely the normal vector to X at p.The Gauss map can be defined...
form:
has normal
.
Derivation of the focus
To derive the focus of a simple parabola, where the axis of symmetry is parallel to the
yaxis with the vertex at (0,0), such as
then there is a point (0,
f)—the focus,
F—such that any point
P on the parabola will be equidistant from both the focus and the linear directrix,
L. The linear directrix is a line perpendicular to the axis of symmetry of the parabola (in this case parallel to the
x axis) and passes through the point (0,
f). So any point
P=(x,y) on the parabola will be equidistant both to (0,
f) and (
x,
f).
FP, a line from the focus to a point on the parabola, has the same length as
QP, a line drawn from that point on the parabola perpendicular to the linear directrix, intersecting at point Q.
Imagine a right triangle with two legs,
x and
fy (the vertical distance between F and P). The length of the hypotenuse,
FP, is given by
(Note that (fy) and (yf) produce the same result because it is squared.)
The line
QP is given by adding y (the vertical distance between the point
P and the xaxis) and f (the vertical distance between the xaxis and the linear directrix).
These two line segments are equal, and, as indicated above, y=ax², thus
Square both sides,
Cancel out terms from both sides,
Divide out the
x² from both sides (we assume that
x is not zero),
So, for a parabola such as f(x)=x², the
a coefficient is 1, so the focus
F is (0,¼)
As stated above, this is the derivation of the focus for a simple parabola, one centered at the origin and with symmetry around the yaxis. For any generalized parabola, with its equation given in the
standard formStandard form may refer to:*The more common name for scientific notation in British English*Standard form – a common form of a linear equation*Canonical form...
,
the focus is located at the point
which may also be written as
and the directrix is designated by the equation
which may also be written as
Reflective property of the tangent
The tangent of the parabola described by equation y=ax
^{2} has slope
This line intersects the
yaxis at the point (0,
y) = (0, 
a x²), and the
xaxis at the point (
x/2,0). Let this point be called
G. Point
G is also the midpoint of line segment
FQ:
Since
G is the midpoint of line
FQ, this means that
and it is already known that
P is equidistant from both
F and
Q:
and, thirdly, line
GP is equal to itself, therefore:
It follows that
.
Line
QP can be extended beyond
P to some point
T, and line
GP can be extended beyond
P to some point
R. Then
and
are
verticalIn geometry, a pair of angles is said to be vertical if the angles are formed from two intersecting lines and the angles are not adjacent. The two angles share a vertex...
, so they are equal (congruent). But
is equal to
. Therefore
is equal to
.
The line
RG is tangent to the parabola at
P, so any light beam bouncing off point
P will behave as if line
RG were a mirror and it were bouncing off that mirror.
Let a light beam travel down the vertical line
TP and bounce off from
P. The beam's angle of inclination from the mirror is
, so when it bounces off, its angle of inclination must be equal to
. But
has been shown to be equal to
. Therefore the beam bounces off along the line
FP: directly towards the focus.
Conclusion: Any light beam moving vertically downwards in the concavity of the parabola (parallel to the axis of symmetry) will bounce off the parabola moving directly towards the focus. (See
parabolic reflectorA parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
.)
The same reasoning can be applied to a parabola whose axis is vertical, so that it can be specified by the equation
.
The tangent has then a generic slope of
.
Reflection derivation, together with trigonometric angle addition rules, leads to the result that the reflected ray has a slope of
.
Another tangent property
Let the line of symmetry intersect the parabola at point
Q, and denote the focus as point
F and its distance from point
Q as
f. Let the perpendicular to the line of symmetry, through the focus, intersect the parabola at a point
T. Then (1) the distance from
F to
T is 2
f, and (2) a tangent to the parabola at point
T intersects the line of symmetry at a 45° angle.
When b varies
The
xcoordinate at the vertex is
, which is found by
derivingIn calculus, a branch of mathematics, the derivative is a measure of how a function changes as its input changes. Loosely speaking, a derivative can be thought of as how much one quantity is changing in response to changes in some other quantity; for example, the derivative of the position of a...
the original equation
, setting the resulting
equal to zero (a
critical pointIn calculus, a critical point of a function of a real variable is any value in the domain where either the function is not differentiable or its derivative is 0. The value of the function at a critical point is a critical value of the function...
), and solving for
. Substitute this
xcoordinate into the original equation to yield:
Simplifying:
Thus, the vertex is at point
Parabolae in the physical world
In nature, approximations of parabolae and paraboloids (such as
catenary curvesIn physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a Ulike shape, superficially similar in appearance to a parabola...
) are found in many diverse situations. The bestknown instance of the parabola in the history of
physicsPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
is the
trajectoryA trajectory is the path that a moving object follows through space as a function of time. The object might be a projectile or a satellite, for example. It thus includes the meaning of orbit—the path of a planet, an asteroid or a comet as it travels around a central mass...
of a particle or body in motion under the influence of a uniform
gravitational fieldThe gravitational field is a model used in physics to explain the existence of gravity. In its original concept, gravity was a force between point masses...
without air resistance (for instance, a baseball flying through the air, neglecting air
frictionFriction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of friction:...
).
The parabolic trajectory of projectiles was discovered experimentally by Galileo in the early 17th century, who performed experiments with balls rolling on inclined planes. He also later proved this mathematically in his book
Dialogue Concerning Two New Sciences. For objects extended in space, such as a diver jumping from a diving board, the object itself follows a complex motion as it rotates, but the
center of massIn physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...
of the object nevertheless forms a parabola. As in all cases in the physical world, the trajectory is always an approximation of a parabola. The presence of air resistance, for example, always distorts the shape, although at low speeds, the shape is a good approximation of a parabola. At higher speeds, such as in ballistics, the shape is highly distorted and does not resemble a parabola.
Another situation in which parabolae may arise in nature is in twobody orbits, for example, of a small planetoid or other object under the influence of the gravitation of the sun. Such parabolic orbits are a special case that are rarely found in nature. Orbits that form a
hyperbolaIn mathematics a hyperbola is a curve, specifically a smooth curve that lies in a plane, which can be defined either by its geometric properties or by the kinds of equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, which are mirror...
or an
ellipseIn geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
are much more common. In fact, the parabolic orbit is the borderline case between those two types of orbit. An object following a parabolic orbit moves at the exact
escape velocityIn physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
of the object it is orbiting, while elliptical orbits are slower and hyperbolic orbits are faster.
Approximations of parabolae are also found in the shape of the main cables on a simple
suspension bridgeA suspension bridge is a type of bridge in which the deck is hung below suspension cables on vertical suspenders. Outside Tibet and Bhutan, where the first examples of this type of bridge were built in the 15th century, this type of bridge dates from the early 19th century...
. The curve of the chains of a suspension bridge is always an intermediate curve between a parabola and a
catenaryIn physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a Ulike shape, superficially similar in appearance to a parabola...
, but in practice the curve is generally nearer to a parabola, and in calculations the second degree parabola is used. Under the influence of a uniform load (such as a horizontal suspended deck), the otherwise hyperbolic cable is deformed toward a parabola. Unlike an inelastic chain, a freelyhanging spring of zero unstressed length takes the shape of a parabola.
Paraboloids arise in several physical situations as well. The bestknown instance is the
parabolic reflectorA parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
, which is a mirror or similar reflective device that concentrates light or other forms of
electromagnetic radiationElectromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space...
to a common
focal pointIn geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This nonideal focusing may be caused by...
. The principle of the parabolic reflector may have been discovered in the 3rd century BC by the geometer
ArchimedesArchimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...
, who, according to a legend of debatable veracity, constructed parabolic mirrors to defend
SyracuseSyracuse is a historic city in Sicily, the capital of the province of Syracuse. The city is notable for its rich Greek history, culture, amphitheatres, architecture, and as the birthplace of the preeminent mathematician and engineer Archimedes. This 2,700yearold city played a key role in...
against the
RomanThe Roman Empire was the postRepublican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
fleet, by concentrating the sun's rays to set fire to the decks of the Roman ships. The principle was applied to
telescopeA telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s in the 17th century. Today, paraboloid reflectors can be commonly observed throughout much of the world in
microwaveMicrowaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
and satellite dish antennas.
Paraboloids are also observed in the surface of a liquid confined to a container and rotated around the central axis. In this case, the
centrifugal forceCentrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
causes the liquid to climb the walls of the container, forming a parabolic surface. This is the principle behind the liquid mirror telescope.
AircraftAn aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
used to create a weightless state for purposes of experimentation, such as
NASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's “
Vomit CometA Reduced Gravity Aircraft is a type of fixedwing aircraft that briefly provides a nearly weightless environment in which to train astronauts, conduct research and film motion pictures....
,” follow a vertically parabolic trajectory for brief periods in order to trace the course of an object in
free fallFree fall is any motion of a body where gravity is the only force acting upon it, at least initially. These conditions produce an inertial trajectory so long as gravity remains the only force. Since this definition does not specify velocity, it also applies to objects initially moving upward...
, which produces the same effect as
zero gravityWeightlessness is the condition that exists for an object or person when they experience little or no acceleration except the acceleration that defines their inertial trajectory, or the trajectory of pure freefall...
for most purposes.
Vertical curves in roads are usually parabolic by design.
Generalizations
In
algebraic geometryAlgebraic geometry is a branch of mathematics which combines techniques of abstract algebra, especially commutative algebra, with the language and the problems of geometry. It occupies a central place in modern mathematics and has multiple conceptual connections with such diverse fields as complex...
, the parabola is generalized by the
rational normal curves, which have coordinates
the standard parabola is the case
and the case
is known as the
twisted cubicIn mathematics, a twisted cubic is a smooth, rational curve C of degree three in projective 3space P3. It is a fundamental example of a skew curve. It is essentially unique, up to projective transformation...
. A further generalization is given by the Veronese variety, when there are more than one input variable.
In the theory of
quadratic formIn mathematics, a quadratic form is a homogeneous polynomial of degree two in a number of variables. For example,4x^2 + 2xy  3y^2\,\!is a quadratic form in the variables x and y....
s, the parabola is the graph of the quadratic form
(or other scalings), while the elliptic paraboloid is the graph of the
positivedefiniteIn mathematics, a definite bilinear form is a bilinear form B over some vector space V such that the associated quadratic formQ=B \,...
quadratic form
(or scalings) and the hyperbolic paraboloid is the graph of the indefinite quadratic form
Generalizations to more variables yield further such objects.
The curves
for other values of
p are traditionally referred to as the
higher parabolas, and were originally treated implicitly, in the form
for
p and
q both positive integers, in which form they are seen to be algebraic curves. These correspond to the explicit formula
for a positive fractional power of
x. Negative fractional powers correspond to the implicit equation
and are traditionally referred to as
higher hyperbolas. Analytically,
x can also be raised to an irrational power (for positive values of
x); the analytic properties are analogous to when
x is raised to rational powers, but the resulting curve is no longer algebraic, and cannot be analyzed via algebraic geometry.
See also
 Catenary
In physics and geometry, the catenary is the curve that an idealised hanging chain or cable assumes when supported at its ends and acted on only by its own weight. The curve is the graph of the hyperbolic cosine function, and has a Ulike shape, superficially similar in appearance to a parabola...
 Ellipse
In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is orthogonal to the cone's axis...
 Hyperbola
In mathematics a hyperbola is a curve, specifically a smooth curve that lies in a plane, which can be defined either by its geometric properties or by the kinds of equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, which are mirror...
 Universal parabolic constant
The universal parabolic constant is a mathematical constant.It is defined as the ratio, for any parabola, of the arc length of the parabolic segment formed by the latus rectum to the focal parameter...
 Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
 Parabolic partial differential equation
A parabolic partial differential equation is a type of secondorder partial differential equation , describing a wide family of problems in science including heat diffusion, ocean acoustic propagation, in physical or mathematical systems with a time variable, and which behave essentially like heat...
 Paraboloid
In mathematics, a paraboloid is a quadric surface of special kind. There are two kinds of paraboloids: elliptic and hyperbolic. The elliptic paraboloid is shaped like an oval cup and can have a maximum or minimum point....
 Quadratic equation
In mathematics, a quadratic equation is a univariate polynomial equation of the second degree. A general quadratic equation can be written in the formax^2+bx+c=0,\,...
 Quadratic function
A quadratic function, in mathematics, is a polynomial function of the formf=ax^2+bx+c,\quad a \ne 0.The graph of a quadratic function is a parabola whose axis of symmetry is parallel to the yaxis....
External links
 Apollonius' Derivation of the Parabola at Convergence
 Interactive paraboladrag focus, see axis of symmetry, directrix, standard and vertex forms
 Archimedes Triangle and Squaring of Parabola at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 Two Tangents to Parabola at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 Parabola As Envelope of Straight Lines at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 Parabolic Mirror at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 Three Parabola Tangents at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 Module for the Tangent Parabola
 Focal Properties of Parabola at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 Parabola As Envelope II at cuttheknot
Cuttheknot is a free, advertisementfunded educational website maintained by Alexander Bogomolny and devoted to popular exposition of many topics in mathematics. The site has won more than 20 awards from scientific and educational publications, including a Scientific American Web Award in 2003,...
 The similarity of parabola at Dynamic Geometry Sketches
 a method of drawing a parabola with string and tacks