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III.4: Amalgamation theorems (Conlon, x 1.3) Many physical and geometrical objects are describable in terms of pieces that are somehow glued together. This principle applies particularly to the theory of smooth manifolds. The purpose of this section is to develop the mathematical concepts and results that are needed to assemble
Sep 24, 2015 · A simple condition is x2 = y3; i.e. whenever a word in x, y contains a term x2 we can write there y3. Thus, we have a new group: x, y: x4, y6, x2 = y3 . In this group, the word x3y3 can be written as x3y3 = x. x2. y3 = x. y3. y3 = xy6 = x simpler expression, because of gluing x2 and y3. In other words, we have "glued" (amal- gum -ated) groups x ...
For example, squares (resp. triangles) have 4 sides (resp. 3 sides); or compact (resp. Lindelöf) spaces are ones where every open cover has a finite (resp. countable) open subcover. sharp Often, a mathematical theorem will establish constraints on the behavior of some object; for example, a function will be shown to have an upper or lower bound.
- Overview
- Euclidean geometry
- Analytic geometry
- Projective geometry
- Differential geometry
- Non-Euclidean geometries
- Topology
- History of geometry
- Ancient geometry: practical and empirical
geometry, the branch of mathematics concerned with the shape of individual objects, spatial relationships among various objects, and the properties of surrounding space. It is one of the oldest branches of mathematics, having arisen in response to such practical problems as those found in surveying, and its name is derived from Greek words meaning “Earth measurement.” Eventually it was realized that geometry need not be limited to the study of flat surfaces (plane geometry) and rigid three-dimensional objects (solid geometry) but that even the most abstract thoughts and images might be represented and developed in geometric terms.
This article begins with a brief guidepost to the major branches of geometry and then proceeds to an extensive historical treatment. For information on specific branches of geometry, see Euclidean geometry, analytic geometry, projective geometry, differential geometry, non-Euclidean geometries, and topology.
In several ancient cultures there developed a form of geometry suited to the relationships between lengths, areas, and volumes of physical objects. This geometry was codified in Euclid’s Elements about 300 bce on the basis of 10 axioms, or postulates, from which several hundred theorems were proved by deductive logic. The Elements epitomized the ax...
Analytic geometry was initiated by the French mathematician René Descartes (1596–1650), who introduced rectangular coordinates to locate points and to enable lines and curves to be represented with algebraic equations. Algebraic geometry is a modern extension of the subject to multidimensional and non-Euclidean spaces.
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Projective geometry originated with the French mathematician Girard Desargues (1591–1661) to deal with those properties of geometric figures that are not altered by projecting their image, or “shadow,” onto another surface.
The German mathematician Carl Friedrich Gauss (1777–1855), in connection with practical problems of surveying and geodesy, initiated the field of differential geometry. Using differential calculus, he characterized the intrinsic properties of curves and surfaces. For instance, he showed that the intrinsic curvature of a cylinder is the same as that of a plane, as can be seen by cutting a cylinder along its axis and flattening, but not the same as that of a sphere, which cannot be flattened without distortion.
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Beginning in the 19th century, various mathematicians substituted alternatives to Euclid’s parallel postulate, which, in its modern form, reads, “given a line and a point not on the line, it is possible to draw exactly one line through the given point parallel to the line.” They hoped to show that the alternatives were logically impossible. Instead...
Topology, the youngest and most sophisticated branch of geometry, focuses on the properties of geometric objects that remain unchanged upon continuous deformation—shrinking, stretching, and folding, but not tearing. The continuous development of topology dates from 1911, when the Dutch mathematician L.E.J. Brouwer (1881–1966) introduced methods gen...
The earliest known unambiguous examples of written records—dating from Egypt and Mesopotamia about 3100 bce—demonstrate that ancient peoples had already begun to devise mathematical rules and techniques useful for surveying land areas, constructing buildings, and measuring storage containers. Beginning about the 6th century bce, the Greeks gathered and extended this practical knowledge and from it generalized the abstract subject now known as geometry, from the combination of the Greek words geo (“Earth”) and metron (“measure”) for the measurement of the Earth.
In addition to describing some of the achievements of the ancient Greeks, notably Euclid’s logical development of geometry in the Elements, this article examines some applications of geometry to astronomy, cartography, and painting from classical Greece through medieval Islam and Renaissance Europe. It concludes with a brief discussion of extensions to non-Euclidean and multidimensional geometries in the modern age.
The origin of geometry lies in the concerns of everyday life. The traditional account, preserved in Herodotus’s History (5th century bce), credits the Egyptians with inventing surveying in order to reestablish property values after the annual flood of the Nile. Similarly, eagerness to know the volumes of solid figures derived from the need to evaluate tribute, store oil and grain, and build dams and pyramids. Even the three abstruse geometrical problems of ancient times—to double a cube, trisect an angle, and square a circle, all of which will be discussed later—probably arose from practical matters, from religious ritual, timekeeping, and construction, respectively, in pre-Greek societies of the Mediterranean. And the main subject of later Greek geometry, the theory of conic sections, owed its general importance, and perhaps also its origin, to its application to optics and astronomy.
While many ancient individuals, known and unknown, contributed to the subject, none equaled the impact of Euclid and his Elements of geometry, a book now 2,300 years old and the object of as much painful and painstaking study as the Bible. Much less is known about Euclid, however, than about Moses. In fact, the only thing known with a fair degree of confidence is that Euclid taught at the Library of Alexandria during the reign of Ptolemy I (323–285/283 bce). Euclid wrote not only on geometry but also on astronomy and optics and perhaps also on mechanics and music. Only the Elements, which was extensively copied and translated, has survived intact.
- Defining Lines. For the following exercises, use this line (Figure 10.4). Figure 10.4. Define DE¯DE¯. Define FF. Define DF↔DF↔. Define EF¯EF¯. Answer.
- Determining the Best Route. View the street map (Figure 10.7) as a series of line segments from point to point. For example, we have vertical line segments AB¯AB¯, BC¯,BC¯, and CD¯CD¯ on the right.
- Identifying Parallel and Perpendicular Lines. Identify the sets of parallel and perpendicular lines in Figure 10.10. Figure 10.10. Answer. Drawing these lines on a grid is the best way to distinguish which pairs of lines are parallel and which are perpendicular.
- Defining Union and Intersection of Sets. Use the line (Figure 10.12) for the following exercises. Draw each answer over the main drawing. Figure 10.12.
Points are precise locations in space, while lines extend infinitely in both directions. By combining these undefined terms, we can define more complex geometric objects. Angles, formed by two rays sharing a common endpoint, allow us to measure rotational relationships. Circles, composed of points equidistant from a central point, form closed ...
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A condition consisting in the combination or union (material, practical, or ideal) of several things; a combination, aggregate, mixture. A composed fabric or structure material or immaterial; a made up whole, a combination, structure, composition. A conjunction, combination, assemblage, united series.
