I think he means the integers are opposites. In other words, if y= -x, then x is the opposite of y. Therefore x= -y and x + y =0. Think of it with numbers. If x = 2, then y = -2 (opposite). If you add opposites you get 0.

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- November 28th 2008, 08:44 AM #1

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## -(a + b) = -a-b

I'm trying to work my way through Basic Mathematics by Serge Lang and am already stuck on page 11!

The part I'm stuck at goes:

-(a + b) = -a - b

Proof. Remember that if x, y are integers then x = -y and y = -x mean that x + y = 0. Thus to prove our assertion, we must show that

(a + b) + (-a - b) = 0

What I'm having trouble understanding is what he means by x and y in this particular case. Does he mean the two expressions? If so, can somebody please point out how the expressions map to x and y?

Thanks.

- November 28th 2008, 04:27 PM #2

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