In
mathematics an
identity is an
equality relation
A =
B, such that
A and
B contain some
variables and
A and
B produce the same value as each other regardless of what values (usually numbers) are substituted for the variables. In other words,
A =
B is an identity if
A and
B define the same
functions. This means that an
identity is an
equality between functions that are differently defined. For example (
a +
b)
2 =
a2 + 2
ab +
b2 and are identities. Identities are sometimes indicated by the
triple bar symbol = instead of =, the
equals sign.