The First Rules for Zero

Having a symbol is one thing; knowing how to calculate with it is another. The breakthrough came from Brahmagupta, an Indian mathematician writing in 628 AD. He set down the first clear rules: zero plus a number is that number, and zero times anything is zero.

He stumbled on one case, though. He claimed that 0 divided by 0 equals 0 — and that snag stayed unresolved for centuries before mathematics settled on the answer we use today: undefined.