There was magic behind what Napier did with equations. He would take one that had some terms equal to some others and by repeated passes of al-jabr bring all the terms to the left, leaving only a zero on the right. These were what he called his ‘equations to nothing’. Why was the trick so important? It depended on what at first seems rather inconsequential: if a product of two or more factors is equal to zero, then at least one of them must be zero as well.
