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Pokhozhaev's identity is an integral relation satisfied by stationary localized solutions to a nonlinear Schrödinger equation or nonlinear Klein–Gordon equation. It was obtained by S.I. Pokhozhaev [1] and is similar to the virial theorem. This relation is also known as G.H. Derrick's theorem. Similar identities can be derived for other ...
Visual proof of the Pythagorean identity: for any angle , the point (,) = (, ) lies on the unit circle, which satisfies the equation + =.Thus, + =. In mathematics, an identity is an equality relating one mathematical expression A to another mathematical expression B, such that A and B (which might contain some variables) produce the same value for all values of the variables ...
where the above convention for the coefficients of the polynomials agrees with the definition of the binomial coefficients, because both give zero for all i > m and j > n, respectively. By comparing coefficients of x r, Vandermonde's identity follows for all integers r with 0 ≤ r ≤ m + n.
Viète obtained his formula by comparing the areas of regular polygons with 2 n and 2 n + 1 sides inscribed in a circle. [ 1 ] [ 2 ] The first term in the product, 2 / 2 {\displaystyle {\sqrt {2}}/2} , is the ratio of areas of a square and an octagon , the second term is the ratio of areas of an octagon and a hexadecagon , etc.
In Cartesian coordinates, the divergence of a continuously differentiable vector field = + + is the scalar-valued function: = = (, , ) (, , ) = + +.. As the name implies, the divergence is a (local) measure of the degree to which vectors in the field diverge.
In linear algebra, a branch of mathematics, the polarization identity is any one of a family of formulas that express the inner product of two vectors in terms of the norm of a normed vector space. If a norm arises from an inner product then the polarization identity can be used to express this inner product entirely in terms of the norm. The ...
The Beltrami identity, named after Eugenio Beltrami, is a special case of the Euler–Lagrange equation in the calculus of variations. The Euler–Lagrange equation serves to extremize action functionals of the form
In mathematics, Sophie Germain's identity is a polynomial factorization named after Sophie Germain stating that + = ((+) +) (() +) = (+ +) (+). Beyond its use in elementary algebra, it can also be used in number theory to factorize integers of the special form +, and it frequently forms the basis of problems in mathematics competitions.