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Quadratic residue
In mathematics, a number q is called a quadratic residue modulo p if there exists an integer x such that:
Otherwise, q is called a quadratic non-residue.
In effect, a quadratic residue modulo p is a number that has a square root in modular arithmetic when the modulus is p. The law of quadratic reciprocity says something about quadratic residues and primes.
Quadratic residues are used in the Legendre symbol. Quadratic reciprocity and the Gauss lemma both reason about quadratic residues.
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09-23-2007 01:00:40
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The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details