negative multiplied by another negative becomes positive; why?

India
June 5, 2011 1:34pm CST
When a negative quantity is multiplied by another negative quantity, the resultant quantity becomes positive. Is it just a universal truth or is there any scientific logic behind it?
1 person likes this
8 responses
@jeffrynov (130)
• Indonesia
5 Jun 11
That is the logical fathom when negative plus negative the results will be positive and otherwise and as example if only two side against each other or in an opposite corelation there will be result as negative
@ravisivan (14079)
• India
5 Jun 11
It is not negative plus negative is positive. It is negative multiplied by negative is positive. A negative five is multiplied by a negative three with an answer of a positive fifteen. This is because each time the negative five is multiplied by another negative number, it is as such changing the negative to a positive - taking away each time a negative and changing the number to a positive.
@dorannmwin (36392)
• United States
7 Jun 11
This is actually something that I really wondered about when I was younger and was learning the rules of mathematics. I actually asked several of my math teachers about this and none of them were really able to explain why things are the way that they are. So, in my life, I've learned that this is just one of the things that you should accept without expecting there to be an explanation as to why it is that way.
@vandana7 (98854)
• India
6 Jun 11
Wish it were true in real life as well. I mean if I hate somebody, and that person hates me back, then it should lead to both us gaining. It doesnt happen that way in real life, does it?
• Philippines
5 Jun 11
I wouldn't know the logic behind it but this information helped me pass my algebra so I have nothing against it.
@stylewaves (1060)
• India
6 Jun 11
It was like as if enemy of and enemy is a friend....:)
@rog0322 (2829)
• Cagayan De Oro, Philippines
6 Jun 11
Hi Doctor, It is a math rule tracing its origins to the number line system. Counting starts with zero and the direction determines its sign. Going to the right, we go higher as positive numbers adds up. Going left, the number gets lower as counting is lessened, thus the negative sign. The result of multiplication, the product, is determined by the two numbers, the factors, actually scaling a number by another in a determined amount. Negatively signed integers to left of the number line get this rule. It is like tracing the origins at the left of the number line and getting the result to right, on the positive zone due to the large scale involved.
@carmelanirel (20942)
• United States
5 Jun 11
Don't question it, accept it... I hate math and though I am learning how to work out some problems, where it comes to adding and subtracting negative numbers, I still have to check my notes to know whether I am to literally add or subtract and what sign to use.. On the other hand, my nine year old son who was never taught how to do this, can do it, no matter what equation I throw at him... That is why I love multiplying and dividing negatives, because I know how to work it out and what sign to use...
@Matpunk85 (1066)
• Italy
5 Jun 11
It's math so for sure there is an explanation, but I must admit I'm not so good in maths and I cannot explain it.