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  2. Envelope (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Envelope_(mathematics)

    In geometry, an envelope of a planar family of curves is a curve that is tangent to each member of the family at some point, and these points of tangency together form the whole envelope. Classically, a point on the envelope can be thought of as the intersection of two " infinitesimally adjacent" curves, meaning the limit of intersections of ...

  3. Derivations of the Lorentz transformations - Wikipedia

    en.wikipedia.org/wiki/Derivations_of_the_Lorentz...

    In the fundamental branches of modern physics, namely general relativity and its widely applicable subset special relativity, as well as relativistic quantum mechanics and relativistic quantum field theory, the Lorentz transformation is the transformation rule under which all four-vectors and tensors containing physical quantities transform from one frame of reference to another.

  4. Formulations of special relativity - Wikipedia

    en.wikipedia.org/wiki/Formulations_of_special...

    Test theories of special relativity are flat spacetime theories which are used to test the predictions of special relativity. They differ from the two-postulate special relativity by differentiating between the one-way speed of light and the two-way speed of light. This results in different notions of time simultaneity.

  5. Variational method (quantum mechanics) - Wikipedia

    en.wikipedia.org/wiki/Variational_method...

    The ground state energy would then be 8E 1 = −109 eV, where E 1 is the Rydberg constant, and its ground state wavefunction would be the product of two wavefunctions for the ground state of hydrogen-like atoms: [2]: 262 (,) = (+) /. where a 0 is the Bohr radius and Z = 2, helium's nuclear charge.

  6. Playfair's axiom - Wikipedia

    en.wikipedia.org/wiki/Playfair's_axiom

    The classical equivalence between Playfair's axiom and Euclid's fifth postulate collapses in the absence of triangle congruence. [18] This is shown by constructing a geometry that redefines angles in a way that respects Hilbert's axioms of incidence, order, and congruence, except for the Side-Angle-Side (SAS) congruence.

  7. Wave equation - Wikipedia

    en.wikipedia.org/wiki/Wave_equation

    The wave equation is a second-order linear partial differential equation for the description of waves or standing wave fields such as mechanical waves (e.g. water waves, sound waves and seismic waves) or electromagnetic waves (including light waves). It arises in fields like acoustics, electromagnetism, and fluid dynamics.

  8. Synthetic geometry - Wikipedia

    en.wikipedia.org/wiki/Synthetic_geometry

    The first systematic approach for synthetic geometry is Euclid's Elements. However, it appeared at the end of the 19th century that Euclid's postulates were not sufficient for characterizing geometry. The first complete axiom system for geometry was given only at the end of the 19th century by David Hilbert. At the same time, it appeared that ...

  9. Analytic geometry - Wikipedia

    en.wikipedia.org/wiki/Analytic_geometry

    In mathematics, analytic geometry, also known as coordinate geometry or Cartesian geometry, is the study of geometry using a coordinate system. This contrasts with synthetic geometry . Analytic geometry is used in physics and engineering , and also in aviation , rocketry , space science , and spaceflight .