Definition:Equals/Historical Note

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Historical Note on Equals

The equals sign was introduced by Robert Recorde in his 1557 work:

The Whetstone of Witte, whiche is the seconde parte of Arithmeteke: containing the extraction of rootes; the cossike practise, with the rule of equation; and the workes of Surde Nombers.

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