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A ray with a terminus at A, with two points B and C on the right. Given a line and any point A on it, we may consider A as decomposing this line into two parts. Each such part is called a ray and the point A is called its initial point. It is also known as half-line, a one-dimensional half-space. The point A is considered to be a member of the ray.
A sphere in 3-space (also called a 2-sphere because it is a 2-dimensional object) consists of the set of all points in 3-space at a fixed distance r from a central point P. The solid enclosed by the sphere is called a ball (or, more precisely a 3-ball). The volume of the ball is given by
A view from inside a 3-torus. All of the cubes in the image are the same cube, since light in the manifold wraps around into closed loops. The three-dimensional torus , or 3-torus , is defined as any topological space that is homeomorphic to the Cartesian product of three circles, T 3 = S 1 × S 1 × S 1 . {\displaystyle \mathbb {T} ^{3}=S^{1 ...
A curve is a 1-dimensional object that may be straight (like a line) or not; curves in 2-dimensional space are called plane curves and those in 3-dimensional space are called space curves. [52] In topology, a curve is defined by a function from an interval of the real numbers to another space. [49]
The principal ray or chief ray (sometimes known as the b ray) in an optical system is the meridional ray that starts at an edge of an object and passes through the center of the aperture stop. [ 5 ] [ 8 ] [ 7 ] The distance between the chief ray (or an extension of it for a virtual image) and the optical axis at an image location defines the ...
A light ray is a line or curve that is perpendicular to the light's wavefronts (and is therefore collinear with the wave vector). A slightly more rigorous definition of a light ray follows from Fermat's principle, which states that the path taken between two points by a ray of light is the path that can be traversed in the least time. [1]
A connected Riemannian manifold (M, g) is said to be symmetric if for every point p of M there exists some isometry of the manifold with p as a fixed point and for which the negation of the differential at p is the identity map. Every Riemannian symmetric space is homogeneous, and consequently is geodesically complete and has constant scalar ...
Conversely, in adding more structure, one may view the plane as a 1-dimensional complex manifold, called the complex line. Many fundamental tasks in mathematics, geometry , trigonometry , graph theory , and graphing are performed in a two-dimensional or planar space.