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Discussion Starter · #1 ·
Can anyone of you explain me this logic of why negative+negative is positive? I was trying to clear it out, but I wasn't getting the apt answer by myself.
 

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Well, first of all this is wrong. A negative plus a negative equals a negative, not a positive. I think what you're trying to refer to is: "negative times negative is positive".

The negative sign is an operator, a symbol which denotes performing a mathematical operation. In this case, the operation is multiplying the number by -1 which changes the sign from either positive to negative or negative to positive. For example, -1 x 25 = -25.

When you multiply two negative numbers there's an additional sign change present. For example, -25 x -5 = 125. If you break it down and consider the integers first and the operators later you get: (25 x 5) x -1 x -1 = 125 x -1 x -1. Then 125 x -1 = -125. And finally -125 x -1 = 125.

Essentially: multiplying a negative by a negative yields a positive. Dividing a negative by a negative yields a positive.
 

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Discussion Starter · #7 ·
Ahh, my bad, I should have written negative times negative=positive.
My concept is much clear now.
Really, thank you for the replies people.
@bluebatteries- Is positive is always on right and negative is always on left in terms of mathematics?
 
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Discussion Starter · #9 ·
Not all feelers requires smiley, logic is enough. :p
 

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The Macabre
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Okay. I'm going to try my hand at an explanation. So, a neg+neg is neg, because it's like giving yourself more neg. A pos is the oppisite of a neg, so neg+pos is like Pos-Pos, or adding less negative. Neg-Neg will give you a positve, because a double negative is postive, like in "I will not not do something." Does that help at all? We're more theroy people, not concrete, so I don't know if we'll be of much help.
 

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Discussion Starter · #14 · (Edited)
Wait... I made sense? [awesome avatar! Internet Farms, go /b/!]
Oh no, I'm sorry but that 'thank you' was for Blue Ocean.I didn't see your post before, but thanks for contributing.I already got the reason! PS- thanks for that avatar compliment :p
 

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Discussion Starter · #19 ·
Okay, I just realized that I've a few more questions regarding the first video.
They've given:

ab+ (-a)(b) + (-a)(-b)
= ab+ -a(+b-b)

what if they had taken the 'ab' as a common? Is it a rule that we can either take a or b as a common? Or the sum wouldn't work if we take it as 'ab'?
 

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Okay, I just realized that I've a few more questions regarding the first video.
They've given:

ab+ (-a)(b) + (-a)(-b)
= ab+ -a(+b-b)

what if they had taken the 'ab' as a common? Is it a rule that we can either take a or b as a common? Or the sum wouldn't work if we take it as 'ab'?
This is a lazy response as I haven't watched the video :p

If you combine the 'ab' terms, this is what you get:

ab + (-ab) + (-a)(-b) = ab - ab + ab = ab

What you've shown above is taking out -a as a common factor which means that the b's cancel out and so you're left with just the ab. If you want to take out the b's instead, you could write the original expression as:

(a-a)(b) + (-a)(-b) = 0 + ab = ab
 
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