# mathematics Were epicycloids from astronomy acceptable curves in Greek geometry? History of Science and Mathematics Stack Exchange

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Curves with eccentricities of more than 1 are even more eccentric. They include points on both sides of the directrix, which could not happen for smaller eccentricities because points on one side of the directrix are necessarily farther from the focus than they are from the directrix. Each part, or branch, is a mirror image of the other; like the ellipse, the hyperbola may be thought of as having two foci and two directrices. Encyclopædia Britannica, Inc.Encyclopædia Britannica, Inc.Any angle smaller than a right angle is acute; those larger than a right angle but smaller than a straight angle are obtuse.

- As it is, with six curves you’ll have six directions.
- We can measure the size of surfaces by calculating their area.
- Like polygons, polyhedra can be named by using Greek numeral prefixes.
- For that to be true, the lines must remain precisely the same distance from each other at every point along their paths.
- In the early 17th century, there were two important developments in geometry.
- The study of the angles of a triangle or of angles in a unit circle forms the basis of trigonometry.
- It would then have another pair of parallel sides and be completely disqualified from being a trapezoid.

String theory makes use of several variants of geometry, as does quantum information theory. Artists have long used concepts of proportion in design. Vitruvius developed a complicated theory of ideal proportions for the human figure. These concepts have been used and adapted by artists from Michelangelo to modern comic book artists. Geometric group theory often revolves around the Cayley graph, which is a geometric representation of a group. Other important topics include quasi-isometries, Gromov-hyperbolic groups, and right angled Artin groups. Discrete geometry includes the study of various sphere packings.

## Geometry – Key takeaways

By the definition above, a vector quantity has both direction and magnitude . A vector can be visualised geometrically as a directed line segment with a length equal to the magnitude of the vector and a direction indicated by an arrow.

- Geometric group theory often revolves around the Cayley graph, which is a geometric representation of a group.
- If you’re working with a fast curve remember that if you keep it at right angles you’ll have a fast curve in a static position, which is almost a contradiction in terms.
- A cross-section is a shape made by cutting through a solid with a plane.

Computational geometry deals with algorithms and their implementations for manipulating geometrical objects. Important problems historically have included the travelling salesman problem, minimum spanning trees, hidden-line removal, and linear programming. In general, algebraic geometry studies geometry through the use of concepts in commutative algebra such as multivariate polynomials. It has applications in many areas, including cryptography and string theory.

## Solids

A three-sided polygon can be called a trigon as part of the name trigonometry, which means “triangle measurement.” Deca- , hendeca- , and dodeca- are also Greek prefixes. These Greek prefixes are used to form the names decagon, hendecagon, and dodecagon. Encyclopædia Britannica, Inc.Encyclopædia Britannica, Inc.People see the many kinds of quadrilaterals more often than they realize. Squares that appear in man-made forms and in the natural world, however, are not usually seen as squares. The first diagram, for example, shows a perspective view of a cubical room, containing a square doorway, a square window, and a square rug. The view is a realistic one, such as a camera would make, and it shows the doorway as an isosceles trapezoid, the window as a right trapezoid, and the floor as a kite. The walls appear as trapezoids that are neither right nor isosceles, and the rug is no special kind of quadrilateral at all.

Skew Lines are two different straight lines in two different directions. Skew the study of curves angles points and lines lines do not lie on the same plane and hence, do not meet each other.

## Lesson Explainer: Points, Lines, and Planes in Space

From the late 1950s through the mid-1970s it had undergone major foundational development, largely due to work of Jean-Pierre Serre and Alexander Grothendieck. This led to the introduction of schemes and greater emphasis on topological methods, including various cohomology theories. One of seven Millennium Prize problems, the Hodge conjecture, is a question in algebraic geometry. Wiles’ proof of Fermat’s Last Theorem uses advanced methods of algebraic geometry for solving a long-standing problem of number theory.

- The secant lines are cut at one point and the two lines form four angles none of which are right angles.
- This means that point 𝑀 lies on all three of these planes.
- A pair of lines that neither intersect nor are parallel to one another are said to be skew.
- Epicycles were viewed as merely computational devices, and their geometry was of little relevance even in geometric constructions used by Ptolemy and his Islamic successors, see e.g.
- A fundamental advance in the theory of curves was the introduction of analytic geometry by René Descartes in the seventeenth century.

Like polygons, polyhedra can be named by using Greek numeral prefixes. The lines are the geometrical one dimensional object with no curve. One dimensional in the sense they have only one dimension, length and no breadth or depth. They are long and straight geometric figures which extend in both the directions.

He proceeded to rigorously deduce other properties by mathematical reasoning. The characteristic feature of Euclid’s approach to geometry was its rigor, and it has come to be known as axiomatic or synthetic geometry. The two dimensions here refer to the length and height of the figure. The point of intersection between the x-axis and the y-axis is called the origin and is denoted by the letter O. Geometry is a branch of mathematics that studies the properties of figures in space. For any two planes, the possible configurations will be coincident, parallel, intersecting at a straight line , or perpendicular.

There are three possible relationships that two lines can have. These lines might intersect at any angle, as demonstrated in the following diagram, or they could be perpendicular (i.e., they intersect orthogonally). In our first two examples, we will demonstrate how to identify a number of lines or planes passing through a point. Recall that for any point in space, there exist an infinite number of lines passing through that point.