Where do math symbols such as + and - come from?

The history of some of the signs is a little fuzzy, but let´s start with the "+" sign for addition, which does seem to have a clear origin. There might be some disputes about details, but the following should give you a decent idea.

The "+" symbol first appeared around 1360 in a manuscript called "Algorismus Proportionum" written by Nicole d´Oresme, a French mathematician. It arose as an abbreviation of "et" which is Latin for"and". With a little imagination you might see how a rapidly scrawled "et" with a badly formed "e" could end up looking like a "+."

The "-" sign for subtraction appears in "Mercantile Arithmetic",written in 1489 by Johannes Widmann, but there are claims that the symbol is older and even goes back to Classical Greece. It may have arisen from being, in a sense, less than a "+" - i.e. missing one line - but the details are lost in history.

The use of a "x" for multiplication dates back to 1631 and William Oughtred´s "Key to Mathematics". It may have originated in tipping over the "+" to represent repeated addition (e.g. 3 x 5 is 3 added to itself 5 times).

The division sign, made of a horizontal line with a dot above it and a dot below it (also called an "obelus") goes back to Johann Rahn in 1659 in a book called "Teutsche Algebra". The slash notation came later, perhaps with the idea that the two things being divided could go where the dots where, and that a slash somehow means cutting or division.

The equals sign "=" has perhaps the nicest story. Robert Recorde, in 1557, wrote in "The Whetstone of Witte" that he would use two parallel lines of equal length to denote equality because "no two things can be more equal than these."

Dr. Knowledge is written by physicists Stephen Reucroft and John Swain, both of Northeastern University. E-mail questions to drknowledge@globe.com or write Dr. Knowledge, c/o The Boston Globe, PO Box 55819, Boston, MA 02205-5819.