#1
Before you ask, yes I have used the search bar ;P

hopefully someone here can explain it to me... I have to prove statements using proofs..but I'm not understanding it at all.
here is an example the teacher gave us

-(a-b)=b-a
1. -(a-b)      1. Given
2. -(a+-b)    2. Subtraction Theorem
3. -1(a+-b)  3. Multpl. Prop of -1
4. -a+b       4. Distrubative property
5. b+-a       5. Communiative Property
6. b-a         6. Subtraction theorem


there was another one... -(-a)=a I had three steps and got it wrong...
Can anyone explain to me how to do these damn things?
btw, i'm in algebra 2
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#3
Quote by thefoundationof
i think i get it so it would be

1. -(-a)=a
2. +a=a
3. a=a

i think i got it right.


I had
1. -(-a)
2. -1(-a)
3. a=a

(Pretty much what you had)
and got it wrong
EDIT: i remember her saying it was 6 steps..
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#4
why oh why do you need 6 steps to prove that? it's practically a given thing in maths in england.
"And after all of this, I am amazed...

...that I am cursed far more than I am praised."
#5
I have no idea. I really don't. She teaches right out of the book, and book doesn't even explain it..so I am really lost at the moment...(with a test coming up on monday! yay!)
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#7
a proof cannot end with the line "0=0"
"And after all of this, I am amazed...

...that I am cursed far more than I am praised."
#9
Quote by thefoundationof
6 steps hmm ok

1.-(-a)=(a)
2.-(-a)-a=a-a
3.-(-a)-a=0
4.-1(-a)-a=0
5.a-a=0
6.0=0

idk im in algebra 1



well...all you'd have to do is add a to the other side.
so 6. would be a=a
but uh...where the hell are you getting those other a's from?
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#10
Quote by Sol9989
why oh why do you need 6 steps to prove that? it's practically a given thing in maths in england.


Basically, you should be able to prove everything you do with the basic axioms.

But I don't really see what these 6 steps in proving -(-a) = a. This is how one of my math professor proved it:

" Thesis: -(-a) = a

The thesis means that the complement of -a, which is -(-a), equals a. This is true, because:

(-a) + a = a + (-a) = 0."
#11
TS are you by any chance a freshman in geometry honors?
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#12
Sophmore in Advanced Algebra
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#14
-(-a) = -(-a) + 0 = -(-a) + (a + (-a)) = (a + (-a)) -(-a) = a + ((-a) - (-a)) = a.