Q: Who invented the equal sign, and...

Q: Who invented the equal sign, and why?

A: Caltech mathematician Tom Apostol says the equal sign was invented by Robert Recorde, the Royal Court physician for England’s King Edward VI and Queen Mary. Recorde lived from 1510 to 1558 and was the most influential English mathematician of his day, although he died in prison for reasons that are not recorded.

In his 1557 book “The Whetstone of Witte,” he wrote: “And 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, of Gemowe [or twin] lines of one lengthe, thus: =====, bicause noe 2 thynges can be moare equalle.”