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  2. Problem of Apollonius - Wikipedia

    en.wikipedia.org/wiki/Problem_of_Apollonius

    To show this, Gergonne considered lines through corresponding points of tangency on two of the given circles, e.g., the line defined by A 1 /A 2 and the line defined by B 1 /B 2. Let X 3 be a center of similitude for the two circles C 1 and C 2; then, A 1 /A 2 and B 1 /B 2 are pairs of antihomologous points, and their lines intersect at X 3. It ...

  3. Line–line intersection - Wikipedia

    en.wikipedia.org/wiki/Lineline_intersection

    Assume that we want to find intersection of two infinite lines in 2-dimensional space, defined as a 1 x + b 1 y + c 1 = 0 and a 2 x + b 2 y + c 2 = 0. We can represent these two lines in line coordinates as U 1 = (a 1, b 1, c 1) and U 2 = (a 2, b 2, c 2). The intersection P′ of two lines is then simply given by [4]

  4. Intercept method - Wikipedia

    en.wikipedia.org/wiki/Intercept_method

    The method yields a line of position (LOP) on which the observer is situated. The intersection of two or more such lines will define the observer's position, called a "fix". Sights may be taken at short intervals, usually during hours of twilight, or they may be taken at an interval of an hour or more (as in observing the Sun during the day).

  5. Projective geometry - Wikipedia

    en.wikipedia.org/wiki/Projective_geometry

    There are two types, points and lines, and one "incidence" relation between points and lines. The three axioms are: G1: Every line contains at least 3 points; G2: Every two distinct points, A and B, lie on a unique line, AB. G3: If lines AB and CD intersect, then so do lines AC and BD (where it is assumed that A and D are distinct from B and C).

  6. Intersection (geometry) - Wikipedia

    en.wikipedia.org/wiki/Intersection_(geometry)

    In geometry, an intersection is a point, line, or curve common to two or more objects (such as lines, curves, planes, and surfaces). The simplest case in Euclidean geometry is the lineline intersection between two distinct lines , which either is one point (sometimes called a vertex ) or does not exist (if the lines are parallel ).

  7. Playfair's axiom - Wikipedia

    en.wikipedia.org/wiki/Playfair's_axiom

    Two straight lines which intersect one another cannot be both parallel to the same straight line. Playfair acknowledged Ludlam and others for simplifying the Euclidean assertion. In later developments the point of intersection of the two lines came first, and the denial of two parallels became expressed as a unique parallel through the given point.

  8. Cayley–Bacharach theorem - Wikipedia

    en.wikipedia.org/wiki/Cayley–Bacharach_theorem

    d = 1: 2 and 1: two points determine a line, two lines intersect in a point, d = 2: 5 and 4: five points determine a conic, two conics intersect in four points, d = 3: 9 and 9: nine points determine a cubic, two cubics intersect in nine points, d = 4: 14 and 16. Thus these first agree for 3, and the number of intersections is larger when d > 3.

  9. Vertex (geometry) - Wikipedia

    en.wikipedia.org/wiki/Vertex_(geometry)

    A vertex of an angle is the endpoint where two lines or rays come together. In geometry, a vertex (pl.: vertices or vertexes) is a point where two or more curves, lines, or edges meet or intersect. As a consequence of this definition, the point where two lines meet to form an angle and the corners of polygons and polyhedra are vertices. [1] [2] [3]