Difference between revisions of "Ring (mathematics)"
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− | '''1.''' ''R'' with addition is a [[commutative]] [[group]]; | + | '''1.''' ''R'' with addition is a [[commutative]] [[Group (mathematics)|group]]; |
'''2.''' ''R'' is closed under multiplication; | '''2.''' ''R'' is closed under multiplication; | ||
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==Examples== | ==Examples== | ||
− | *<math>(\mathbb{Z},+, \cdot)</math> - the set of the integers - together with the usual [[addition]] and [[multiplication]] is a ring. | + | *<math>(\mathbb{Z},+, \cdot)</math> - the set of the [[integers]] - together with the usual [[addition]] and [[multiplication]] is a ring. |
*the [[subring]] of the even numbers is a ring, too: this shows that there is not necessarily a neutral element of the multiplication in a ring. | *the [[subring]] of the even numbers is a ring, too: this shows that there is not necessarily a neutral element of the multiplication in a ring. | ||
*<math>(\mathbb{Z} / 6\mathbb{Z},+, \cdot)</math> : this is the ring of six elements {0,1,2,3,4,5} and the usual addition and multiplication [[modulo]] six. So, here 1+3= 4, but 4+5 = 3. Interestingly, <math>2 \cdot 3 = 0 </math>, so, you can multiply two elements, neither of which is zero, and get zero as the result! | *<math>(\mathbb{Z} / 6\mathbb{Z},+, \cdot)</math> : this is the ring of six elements {0,1,2,3,4,5} and the usual addition and multiplication [[modulo]] six. So, here 1+3= 4, but 4+5 = 3. Interestingly, <math>2 \cdot 3 = 0 </math>, so, you can multiply two elements, neither of which is zero, and get zero as the result! | ||
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A '''commutative ring''' is a ring in which multiplication is commutative. | A '''commutative ring''' is a ring in which multiplication is commutative. | ||
− | A '''division ring''' is a ring such that ''R'' with multiplication is a (not necessarily [[commutative]]) [[group]]. | + | A '''division ring''' is a ring such that ''R'' with multiplication is a (not necessarily [[commutative]]) [[Group (mathematics)|group]]. |
[[Category:Algebra]] | [[Category:Algebra]] |
Revision as of 21:01, November 17, 2008
A ring in mathematics is a set R equipped with two binary operations, usually called addition and multiplication, satisfying that
1. R with addition is a commutative group;
2. R is closed under multiplication;
3. Multiplication is associative;
4. Multiplication distributes over addition.
Examples
- - the set of the integers - together with the usual addition and multiplication is a ring.
- the subring of the even numbers is a ring, too: this shows that there is not necessarily a neutral element of the multiplication in a ring.
- : this is the ring of six elements {0,1,2,3,4,5} and the usual addition and multiplication modulo six. So, here 1+3= 4, but 4+5 = 3. Interestingly, , so, you can multiply two elements, neither of which is zero, and get zero as the result!
Remarks
A ring with unity is a ring for which multiplication has a neutral element.
A commutative ring is a ring in which multiplication is commutative.
A division ring is a ring such that R with multiplication is a (not necessarily commutative) group.