I have problem with proofs in vector space. First is
$\vec x+(-(\vec y+\vec z))=(\vec x+(-\vec y))+(-\vec z)$
and the second
$a\cdot \vec x+b \cdot \vec y=b \cdot \vec x+a\cdot \vec y \Leftrightarrow a=b \vee \vec x=\vec y $
Could anyone help me with this? I'm sorry for my bad english.
In the second task I have:
$a\cdot \vec x+b \cdot \vec y $ I have sentece that $ \vec x = \vec y$ or $a=b$
So i'm changing $ \vec y $ on $ \vec x$
$a\cdot \vec x+b \cdot \vec x = (a+b)\vec x = (a+b) \vec y =...$
And i don't know what can i do next.