minus into minus is equal to plus
By agladiator
@agladiator (233)
Bangladesh
July 6, 2008 6:18am CST
hi everyone.
first thing do you love math. i love it. i have a question to everybody. in the school we all read the algebra. there we learn minus into minus is equal to plus. now my question is do you really know why minus into minus is equal to plus. if you know the ans then please share with me. i know how it is. but its very complex. i solve this by complex veriable. if you know any easy answer about it then please tell me. if you do not know then response here, i want to know how many do not know this..
3 responses
@iabbo83 (47)
• Italy
15 Jul 08
I have said a nonsense! This is the demostration:
Why must to enlarge the definition of product from N to Z (Natural - Integers)
maintaining the properties of the operation of product: Commutative and the Law annulment product : XY = YX ; Y*0 = 0.
We know that 2*3 = 2 + 2 + 2 so in Z:
2*3=6 and +*+ = + naturally
(-3)*2 = (-3)*(-3)*(-3)=-6
2*(-3) = (-3)*(2) = -6 for the commutative property so we demonstrate that for all x,y in Z (-x) * (+y) = - (XY)
Now for(-x)*(-y) why use the Law annulment product and the property :
x*(y + z) = x*y + x*z (1)
step 1:
we know that:
(-x)*(-y + y) = -x * 0 = 0 so from the property (1)
(-x)*(-y) + (-x)*(y) = 0 we have demostrate that (-x)*(y)=-(x*y)
so we have
(-x)*(-y) -(x*y) = 0
if we call z = (-x)*(-y) so z-(x*y) = 0
we must to search z:
we know that z = x * y
so we demostrate that minus * minus = plus for every x,y in Z
@graceandowen (1637)
•
6 Jul 08
i remember hearing something about 2 minus always make a positive, not a clue tho why that is, take me back a few years when i was at school and i could have probably told you the answer but my brain is now like a sieve and i dont remember much lol!
maths was never a fave subject of mine but i was good at it, i hated it so much tho that i did the bare min to pass the gcse
@agladiator (233)
• Bangladesh
6 Jul 08
hm if you practicing math then your brain not becomes a sieve. i think math is like our life.
@mikedotcom (260)
• United States
9 Jul 08
Informally, we might look at this:
I assume you have belief that... +12/(+3)= +4
then it "makes sense" that... +12/(-3)= -4
because minus means opposite, and if you divide by a negative, your answer should be the opposite too.
So, climbing the ladder of reasoning...-12/(-3)= -(-4)
because like above, the answer will be the opposite.
But what is the opposite of negative?
Clearly it is positive, thus -(-4) is +4
and the question -12/(-3)= +4 is very reasonable!
I hope "divided by" is ok to substitute for "goes into" for the sake of this discussion, cause I couldn't find the "goes into" key on my keyboard!
