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In mathematics, the law of signs governs multiplication of positive and negative numbers.
Thomas Harriot and Girolamo Cardano considered alternate versions of multiplication in which minus times minus equals minus.[1][2]
References[edit]
- Arcavi, Abraham; Bruckheimer, Maxim (November 1981), "How Shall We Teach the Multiplication of Negative Numbers?", Mathematics in School, 10 (5): 31–33, doi:10.2307/30214312
- Peterson, John C. (May 1972), "Fourteen different strategies for multiplication of integers or why (⁻1) (⁻1) = ⁺1", The Arithmetic Teacher, 19 (5): 396–403, doi:10.2307/41188049
- Tanner, R. C. H. (March 1980a), "The Ordered Regiment of the Minus Sign: Off-Beat Mathematics in Harriot's Manuscripts", Annals of Science, 37 (2): 127–158, doi:10.1080/00033798000200161
- Tanner, R. C. H. (March 1980b), "The Alien Realm of the Minus: Deviatory Mathematics in Cardano's Writings", Annals of Science, 37 (2): 159–178, doi:10.1080/00033798000200171