$-a=(-1)\cdot a,\forall a\in\mathbb{R}$ using axioms

I've been trying to prove$$-a=(-1)\cdot a$$for every $a\in\mathbb{R}$ using only axioms, however, every demonstration I found use one of these two properties:$$0\cdot a=0,\quad\forall a\in\mathbb{R}$$or the uniqueness of $-a$ such that$$a+(-a)=0$$

Is there a way to not use them?