- #1
homology
- 306
- 1
So I'm teaching a college algebra course this summer and I'm trying to go nice and slow and give good reasons for most things. One thing I can't seem to justify is why (-1)(-1)=1. I can do it with equivalence class (pairs of natural numbers) or the following little proof but I'd like to have a good grounded explanation (like you can use holes and piles of dirt for adding negative and positive numbers together).
1-1=0
-1(1-1)=0
(-1)(1)+(-1)(-1)=0
(-1)(-1)=1
So does anyone have a nice meat and potato way of explaining it?
1-1=0
-1(1-1)=0
(-1)(1)+(-1)(-1)=0
(-1)(-1)=1
So does anyone have a nice meat and potato way of explaining it?
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