# Message Board

 Message Board > Malarkey > Simple subtraction question

 April 15, 2013, 17:27 Zomg None 641 posts On a number line, when you subtract, you go to the left from 0. When you add, you go to the right from zero. But when you do e.g. 8- -2, how do you move -2 places? Why does - - result in +? While any valid answer is welcome, I would much prefer answers in the style of ontological proofs: http://www.scribd.com/doc/6194 … Complex-Numbers Thank you. ____________ #
 April 17, 2013, 14:05 Dennis どこかにいる 2050 posts Substracting is just adding negative numbers. 5-2 = 5+(-2) a "-" as a sign could also be seen as "-1 times" -5 = (-1)*5 a "-" as operator could be seen as "adding -1 times" 5-2 = 5+ ((-1)*2) Agreeing on that you can do this: 8-(-2) = 8 + ((-1)*(-1)*2) <=> 8-(-2) = 8 + ((-1)*(-1)*2) <=> 8-(-2) = 8 + (1*2) <=> 8-(-2) = 8 + (1*2) <=> 8-(-2) = 8 + (2) <=> 8-(-2) = 8 + 2 <=> 8-(-2) = 10[Edited on April 17, 2013 by Dennis] ____________ Kwakkel #
 April 17, 2013, 14:18 Dennis どこかにいる 2050 posts Be aware that there is a difference between "-" as an operator and "-" as a sign. The sign just tells something about the number (it's minus 5 degrees) meaning it is lower than zero. It isn't that special because if I added a number to each term in the equation the result wouldn't change. 10-5 = 5 add 20 30-25 = 5 add 1 11-6 = 5 add 1000 1010 - 1005 = 5 the result will never change no matter wht you add to both terms. x = 8-(-2) x = (8+10)-((-2)+10) //I add 10 to both terms x = (18) - (8) x = 10 ____________ Kwakkel #
 April 17, 2013, 17:21 Zomg None 641 posts Very nice work Dennis.. I guess those mathematics hours at high school paid off huh? :o What does <=> mean? "if and only if"? Dennis, could you please tell me if this is correct: http://www.youtube.com/watch?v=oZ8S0--fj8g Zank yuu. ____________ #
 April 18, 2013, 10:54 Dennis どこかにいる 2050 posts lol @ hax00rify It seems correct. it means "if and only if" ____________ Kwakkel #
 April 18, 2013, 11:00 Zomg None 641 posts hax00rify is my clandestine account I use for uploading videos to show to people (strangers) on the internet (I know you're not a stranger but yeah =P) so that they can't track who I am. I posted that video on some other forums as well. =) ____________ #

Message Board > Malarkey > Simple subtraction question