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  2. Raising and lowering indices - Wikipedia

    en.wikipedia.org/wiki/Raising_and_lowering_indices

    It is common convention to use greek indices when writing expressions involving tensors in Minkowski space, while Latin indices are reserved for Euclidean space. Well-formulated expressions are constrained by the rules of Einstein summation : any index may appear at most twice and furthermore a raised index must contract with a lowered index.

  3. Snell's law - Wikipedia

    en.wikipedia.org/wiki/Snell's_law

    Refraction of light at the interface between two media of different refractive indices, with n 2 > n 1.Since the velocity is lower in the second medium (v 2 < v 1), the angle of refraction θ 2 is less than the angle of incidence θ 1; that is, the ray in the higher-index medium is closer to the normal.

  4. Fermi problem - Wikipedia

    en.wikipedia.org/wiki/Fermi_problem

    A Fermi problem (or Fermi question, Fermi quiz), also known as an order-of-magnitude problem, is an estimation problem in physics or engineering education, designed to teach dimensional analysis or approximation of extreme scientific calculations. Fermi problems are usually back-of-the-envelope calculations.

  5. Quizlet - Wikipedia

    en.wikipedia.org/wiki/Quizlet

    Quizlet was founded in October 2005 by Andrew Sutherland, who at the time was a 15-year old student, [2] and released to the public in January 2007. [3] Quizlet's primary products include digital flash cards , matching games , practice electronic assessments , and live quizzes.

  6. How to Solve It - Wikipedia

    en.wikipedia.org/wiki/How_to_Solve_It

    How to Solve It suggests the following steps when solving a mathematical problem: . First, you have to understand the problem. [2]After understanding, make a plan. [3]Carry out the plan.

  7. Miller index - Wikipedia

    en.wikipedia.org/wiki/Miller_index

    Examples of determining indices for a plane using intercepts with axes; left (111), right (221) There are two equivalent ways to define the meaning of the Miller indices: [1] via a point in the reciprocal lattice, or as the inverse intercepts along the lattice vectors. Both definitions are given below.

  8. Frobenius method - Wikipedia

    en.wikipedia.org/wiki/Frobenius_method

    Some solutions of a differential equation having a regular singular point with indicial roots = and .. In mathematics, the method of Frobenius, named after Ferdinand Georg Frobenius, is a way to find an infinite series solution for a linear second-order ordinary differential equation of the form ″ + ′ + = with ′ and ″.

  9. Atiyah–Singer index theorem - Wikipedia

    en.wikipedia.org/wiki/Atiyah–Singer_index_theorem

    The index problem is the following: compute the (analytical) index of D using only the symbol s and topological data derived from the manifold and the vector bundle. The Atiyah–Singer index theorem solves this problem, and states: The analytical index of D is equal to its topological index.