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  2. Monge's theorem - Wikipedia

    en.wikipedia.org/wiki/Monge's_theorem

    The three apex points always define a plane in three dimensions, and all three centers of similarity must lie in the plane containing the circular bases. Hence, the three centers must lie on the intersection of the two planes, which must be a line in three dimensions. [2] Monge's theorem can also be proved by using Desargues' theorem.

  3. Parallel (geometry) - Wikipedia

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

    Line m is in the same plane as line l but does not intersect l (recall that lines extend to infinity in either direction). When lines m and l are both intersected by a third straight line (a transversal ) in the same plane, the corresponding angles of intersection with the transversal are congruent .

  4. 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]

  5. Vanishing point - Wikipedia

    en.wikipedia.org/wiki/Vanishing_point

    All vanishing points associated with different lines with different slopes belonging to plane π will lie on the x′ axis, which in this case is the horizon line. 2. Let A , B , and C be three mutually orthogonal straight lines in space and v A ≡ ( x A , y A , f ) , v B ≡ ( x B , y B , f ) , v C ≡ ( x C , y C , f ) be the three ...

  6. Line–plane intersection - Wikipedia

    en.wikipedia.org/wiki/Lineplane_intersection

    The three possible plane-line relationships in three dimensions. (Shown in each case is only a portion of the plane, which extends infinitely far.) In analytic geometry, the intersection of a line and a plane in three-dimensional space can be the empty set, a point, or a line. It is the entire line if that line is embedded in the plane, and is ...

  7. Intersection (geometry) - Wikipedia

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

    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). Other types of geometric intersection include: Lineplane intersection; Line–sphere intersection; Intersection of a polyhedron with a line

  8. 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).

  9. 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.