Addition by subtraction: does this saying have any mathematical meaning?

Question

I recently read an article that uses the phrase "addition by subtraction", the idea that value may be gained by losing something of negative value. While I doubt this has literal meaning in mathematics, does this idea have any relevance in mathematics?

score 1 · Answer 1 · answered Dec 18 '17 at 19:25

1

Of course it has a literal meaning in mathematics. 5-(-5)=+10.
If you subtract a negative number, this always happens.

answered Dec 18 '17 at 19:25

Kostis Pet

11

This is multiplication and not "addition by subtraction". – footose May 26 '22 at 16:15

score 1 · Accepted Answer · answered Apr 02 '14 at 05:28

Well sure. If I'm trying to make a quantity $x−y$ bigger, one way is to make $x$ bigger. The other is to make $y$ smaller. More precisely, we say that $(x,y) \mapsto x-y$ is monotone in the first argument, and antitone in the second. (The monotone/antitone terminology is not completely standardized).

Addition by subtraction: does this saying have any mathematical meaning?

2 Answers2