this is valid?

Semidevil

Diamond Member
Apr 26, 2002
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prove that -(-a) = a.

my proof is that

-(-a) = -1*(-a) = -(-1*a) = -(-(1*a)) = a.

this is assuming we are using a bunch of already proved properties, i.e, they commute, and there exists a 1 identity..etc etc...

if this is wrong, any tips?
 

Cobalt

Diamond Member
Apr 3, 2000
4,642
1
81
Negative multiplied by a negative equals a positive. I don't see what the problem is.
 

Semidevil

Diamond Member
Apr 26, 2002
3,017
0
76
this is homework guys...not too much time.

anyways, yea, we all know that negative * negative is positive, and I just want to make sure when I write down this proof, because I want to be as precise as possible......not leave any details out.
 

Cristatus

Diamond Member
Oct 13, 2004
3,908
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welll.....since a = 1a, and -a = -1a, --a = a, and --1a = a, which is the same thing, yes :D but it's just pointless to do that unless you are a 6th/7th grade textbook

edit: speeling mistakes
 

Cobalt

Diamond Member
Apr 3, 2000
4,642
1
81
Originally posted by: logic1485
welll.....since a = 1a, and -a = -1a, --a = a, and --1a = a, which is the same thing, yes :D but it's just pointless to do that unless you are a 6th/7th grade textbook

edit: speeling mistakes

Edit didn't work so well now did it? :eek: