Thoughts on Why (–1)(–1) = +1
December 2008, Volume 102, Issue 5, Page 374
Consider why (–1)(–1) = +1 and how and why a teacher might go about explaining this concept to high school students without using pseudoreasoning. Also a precise explanation, through the use of the distributive property, as to why (–1)(–1) = +1.
Numbers and Operations
Reasoning and Proof