Which of these mathematical symbols was first used by Johann Rahn and John Pell?
Johann Heinrich Rahn (10 March 1622 – 25 May 1676) was a Swiss mathematician who is usually credited with the first use of the division sign, “÷”. The symbol appeared in “Teutsche Algebra”, published in 1659. John Pell (1 March 1611 – 12 December 1685), an English mathematician and political agent, collaborated with Rahn on this book, and it is uncertain whether it was Rahn or Pell who was principally responsible for introducing the symbol.
The familiar form “÷” is a repurposed variant of a symbol known as an obelus which comes from “ὀβελός” (“obelós”), the Ancient Greek word for a sharpened stick, spit, or pointed pillar. This is the same root as that of the word “obelisk.”
The modern mathematical symbol “÷” is used in anglophone countries as a division sign. However, this usage is neither universal nor recommended: the ISO 80000-2 standard for mathematical notation recommends only the solidus “/” or fraction bar for division, or the colon “:” for ratios; it says that “÷” should not be used for division.