In ring $(R,+,*)$, the minus sign is often given as a unary operator for the additive inverse such that:
$\forall x\in R (-x\in R)$
$\forall x\in R(x+(-x)=0 \wedge (-x)+x=0)$
If we have $-x\in R$, can we prove (or assume) that $x\in R$?
EDIT: Although it is really Limitless's subsequent comment that I am accepting, I have indicated acceptance of his/her answer.