Minus times minus
Sep. 15th, 2006 12:08 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
jackCan you remember when you first learnt/understood that a negative number times a negative number gave a positive number?
Did you think that makes sense? Did you think it should be negative, or were you just not sure?
I'm sure I'd learnt the rule before then, but I remember working out an explanation for why it makes sense (imagine you give out numbers of merits or demerits to people; taking back a number of demerits is the same as giving that number of merits). Before then, I didn't see why it should be positive, though I don't think I thought it should be be negative, I just didn't understand why.
Conversely, some people think the other way round. Negative Math: How Mathematical Rules Can Be Positively Bent. I haven't read all of his book, so I don't know if it's a good explanation of why and how mathematical rules are chosen, or if he's smoking bad weed. It could be either.
I do know it made me queasy. He seems to think minus times minus giving minus is more obvious, and perhaps should be standard, and that mathematics is a conspiracy against this.
Did you think that makes sense? Did you think it should be negative, or were you just not sure?
I'm sure I'd learnt the rule before then, but I remember working out an explanation for why it makes sense (imagine you give out numbers of merits or demerits to people; taking back a number of demerits is the same as giving that number of merits). Before then, I didn't see why it should be positive, though I don't think I thought it should be be negative, I just didn't understand why.
Conversely, some people think the other way round. Negative Math: How Mathematical Rules Can Be Positively Bent. I haven't read all of his book, so I don't know if it's a good explanation of why and how mathematical rules are chosen, or if he's smoking bad weed. It could be either.
I do know it made me queasy. He seems to think minus times minus giving minus is more obvious, and perhaps should be standard, and that mathematics is a conspiracy against this.
For the record
Date: 2006-09-15 11:23 am (UTC)2. There are many reasons I like the normal way. It makes balance sheets calculatable. It makes algabraic rules most consistent.
3. But I don't know if another way could be useful for some things or not. Apparently he constucts an algebra such as he describes. I thought I'd worked out what it must be but now I'm not sure. I think addition works the same way, the positive numbers work the same way, but something nasty happens to distributivity with negative numbers (else you get contradictions).