Using the wikipedia axioms:
>>6 -0=0
0 + (-0) = 0 (axiom 4, additive inverse)
-0 = 0 (axiom 3, additive identity)
>>10 -x = (-1)x
This one is a bit long, there is probably a shorter way. First we need to show that 0x = 0.
Note that the two zeros are different though, one is a scalar, the other is a vector.
0 + 0 = 0 (field axiom additive identity, these are scalars)
(0 + 0)x = 0x (acting on x)
0x + 0x = 0x (axiom 6 distributivity)
(0x + 0x) + -(0x) = 0x + -(0x) (Add -(0x) to both sides, use axiom 4 for existence)
0x + (0x + -(0x)) = 0x + -(0x) (axiom 1 associativity)
0x + 0 = 0 (Axiom 4 additive inverse)
0x = 0 (Axiom 3 additive identity)
Now the rest follows easily
(1 + -1) x = 0 (field axiom, additive inverse)
1x + (-1)x = 0 (axiom 6 distributivity)
x + (-1)x = 0 (axiom 8 scalar multiplication identity)
Hence (-1)x is an additive inverse of x, so by axiom 4
(-1)x = -x