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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 ...
A general form, also known as the Cauchy–Binet formula, states the following: Suppose A is an m×n matrix and B is an n×m matrix. If S is a subset of {1, ..., n} with m elements, we write A S for the m×m matrix whose columns are those columns of A that have indices from S.
The six trigonometric functions are defined for every real number, except, for some of them, for angles that differ from 0 by a multiple of the right angle (90°). Referring to the diagram at the right, the six trigonometric functions of θ are, for angles smaller than the right angle:
These identities are useful whenever expressions involving trigonometric functions need to be simplified. An important application is the integration of non-trigonometric functions: a common technique involves first using the substitution rule with a trigonometric function, and then simplifying the resulting integral with a trigonometric identity.
Another method of deriving vector and tensor derivative identities is to replace all occurrences of a vector in an algebraic identity by the del operator, provided that no variable occurs both inside and outside the scope of an operator or both inside the scope of one operator in a term and outside the scope of another operator in the same term ...
Comment: The proof of Euler's four-square identity is by simple algebraic evaluation. Quaternions derive from the four-square identity, which can be written as the product of two inner products of 4-dimensional vectors, yielding again an inner product of 4-dimensional vectors: (a·a)(b·b) = (a×b)·(a×b).
In combinatorics, the hockey-stick identity, [1] Christmas stocking identity, [2] ... The inductive and algebraic proofs both make use of Pascal's identity:
The second identity is the so-called push-through identity [7] (+) = (+) that we obtain from (+) = (+) after multiplying by (+) on the right and by (+) on the left. Putting all together, ( I + U V ) − 1 = I − U V ( I + U V ) − 1 = I − U ( I + V U ) − 1 V . {\displaystyle \left(I+UV\right)^{-1}=I-UV\left(I+UV\right)^{-1}=I-U\left(I+VU ...