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Inverse may refer to:
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In many contexts in mathematics the term inverse indicates the opposite of something. This word and its derivatives are used widely in mathematics, as illustrated below.
In abstract algebra, the idea of an inverse element generalises concepts of a negation (sign reversal) in relation to addition, and a reciprocal in relation to multiplication. The intuition is of an element that can 'undo' the effect of combination with another given element. While the precise definition of an inverse element varies depending on the algebraic structure involved, these definitions coincide in a group.
The word 'inverse' is derived from Latin: inversus that means 'turned upside down', 'overturned'.
Let be a set with a binary operation
(i.e., a
magma note that a magma also has closure under the binary operation). If is an identity element of
(i.e., S is a unital magma) and
, then
is called a left inverse of
and
is called a right inverse of
. If an element
is both a left inverse and a right inverse of
, then
is called a two-sided inverse, or simply an inverse, of
. An element with a two-sided inverse in
is called invertible in
. An element with an inverse element only on one side is left invertible, resp. right invertible. A unital magma in which all elements are invertible is called a loop. A loop whose binary operation satisfies the associative law is a group.