The Whetstone of Witte: whiche is the seconde parte of arithmetike; containyng thextraction of rootes: the cossike practise, with the rule of equation: and the woorkes of surde nombers

'The Whetstone of Witte' was published in 1557 and written by the influential Welsh mathematician and teacher Robert Recorde. It is in this book that algebra and the equals sign (=) are introduced for the first time in published form.