Satisfiability of a field axiom, given model Considering the following field axiom:
$\forall$$x((x\neq0) \rightarrow \exists y(x.y=1))$
I am trying to show that this axiom is true for the model R = ($\mathbb{R}, 0, 1, +, .)$ 
Using some rules of satisfiability. Let (M, v) be a generic L-Model, then:
$(M, v) \vDash \forall$$x((x\neq0) \rightarrow \exists y(x.y=1))$ iff
$(M, [v]^{a}_x) \vDash $ $(x\neq0) \rightarrow \exists y(x.y=1)$, for all a $\in \mathbb{R} $
So:
1 - $(M, [v]^{a}_x) \vDash $ $¬(x\neq0) $, for all a $\in \mathbb{R} $
or
2 - $(M, [v]^{a}_x) \vDash $ $ \exists y(x.y=1)$, for all a $\in \mathbb{R} $
Considering 1, simplifying the expression:
$(M, [v]^{a}_x) \vDash $ $(x=0) $, for all a $\in \mathbb{R} $. So  $a = 0$ for all a $\in \mathbb{R} $ is false.
Considering 2, we have:
$(M, [v]^{a}_x) \vDash $ $ \exists y(x.y=1)$, for all a $\in \mathbb{R} $
$(M, [v]^{a b}_{x y}) \vDash $ $(x.y=1)$, for all a $\in \mathbb{R} $, for some b $\in \mathbb{R} $. Finally:
$a.b=1$, for all a $\in \mathbb{R} $, for some b $\in \mathbb{R} $. This is not true when $a=0$.
So neither 1 or 2 are true following the above solution. What am I doing wrong in this case?

You want to show that for every $a\in \mathbb{R}$ either 1 or 2 true is the case. You are correctly claiming that 2 is not the case only if $a=0$, but it is preceisely the case where 1 is true, so actually have shown what you wanted.In more details: if $a=0$ then really $(M,[v]^a_x)\nvDash \exists y (x*y=1)$ however 1 is true, meaning that $(M,[v]^a_x)\models x=0$, which is enough to conclude $(M,[v]^a_x)\models x\neq 0\to \exists y(y*x=1)$. 
