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Why negative times negative is positive 
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#1
Feb2412, 10:34 AM

P: 8

hey friend can anybody give answer?
why () * () = (+) 


#2
Feb2412, 11:09 AM

Math
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Thanks
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P: 39,491

Its impossible to give an explanation that you would accept without knowing what kind of explanation you would accept!
For example, one can show that a(b+ c)= ab+ ac (the "distributive law"). In particular, if we take a=x, b=y, c= y, that says x(y+ (y))= x(y)+ (x)(y). But y+(y)= 0 and x(0)= 0 so that tells us that x(y)+ (x)(y)= 0. Adding x(y) to both sides, x(y)= x(y). Is that acceptable? 


#3
Feb2412, 11:16 AM

HW Helper
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P: 1,961

Think of a as a reflection of a through the origin. Reflecting twice gives you back a: (a) = a.



#4
Feb2512, 10:42 AM

P: 8

Why negative times negative is positive
i was cleared after going through this.
http://www.mathsisfun.com/multiplyingnegatives.html 


#5
Feb2512, 11:09 AM

P: 225

nice link 


#6
Feb2612, 04:51 AM

P: 318

I have a simple explanation if u confined to Integers only
first of u need to know why  * + =  multiplication is seemed to be derived from addition. Like2*3=2+2+2. and 3+4=3+3+3+3.. So when u write (3)*4= (3)+ (3)+ (3)+ (3)= (12) hence it is proved that ()* (+)= () Now come to ()* ()= (+) Let me say u want to solve the question something like this. (1)/1. you must have done divisions in primary classes where you make make a pie ∏ shape. write denominator part inside and numerator part outside etc,.. when u do such ting with (1)/1. then u have two choices for quotient 1 or (1). If u put 1 then using quotient rule. 1*(1)+0=1 . But it's wrong so 1 is only answer u can think of.. All this is poor explanation since real numbers and complex number are not taken. similar about others... 


#7
Feb2612, 09:02 AM

P: 327



#8
Feb2912, 12:12 AM

P: 8

mathforum is also not bad..



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