# Definition:Equals

## Definition

The symbol $=$ means equals.

$x = y$ means $x$ is the same object as $y$, and is read $x$ equals $y$, or $x$ is equal to $y$.
$x \ne y$ means $x$ is not the same object as $y$, and is read $x$ does not equal $y$, or $x$ is not equal to $y$.

The expression:

$a = b$

means:

$a$ and $b$ are names for the same object.

## Note on Terminology

Two objects being equal is not necessarily the same as two objects being congruent.

This distinction is often not made.

When such a difference is important the symbol $=$ may be used for equal and $\cong$ for congruent.

## Historical Note

The equals sign was introduced by Robert Recorde in his $1557$ work The Whetstone of Witte.

Placing two long hyphens together, one above the other, he wrote:

To avoide the tediouse repetition of these woordes: is equalle to: I will sette as I doe often in woorke use, a paire of paralleles, or gemowe lines of one lengthe: $= \!\!\! = \!\!\! = \!\!\! = \!\!\! = \!\!\! = \!\!\! =$, bicause noe .2. thynges, can be moare equalle.

The word gemowe comes from the Latin geminus meaning twin.

François Viète used the symbol $\sim$, while René Descartes used $\propto$.

Both were in due course supplanted by $=$, a shortened and hence more efficient version of Recorde's invention.

It is suggested by some sources that this was mainly through the influence of Leibniz.

## Linguistic Note

The word equality is the noun derived from the adjective equal.

The word equals has the verb form equate, which means to state that one expression is equal to another expression.

Hence to equate means to form an equation.