u/Bloomichat

I'm struggling a lot with basic mathematics by Serge Lang. Particularly with this N7 and N8 proofs

1 I don't understand how I am supposed to solve them, do I have to read a previous book in order to prove the proofs? Am I not ready to continue this just yet?

2 How am I actually supposed to use N7 and N8?. Like, how do I apply it to exercises? I don't find a use for them

N7 is (-1)a = -a

N8 is -(ab) = (-a)b