I have to express $x\geq 0$ given only the binary operations of addition ($*$) and multiplication ($\circ$) on the reals, and equality. For example, I could say that $x=0$ by writing $\forall y(x\circ y=x)$. Alternatively, I could say $\forall y(x*y=y).$ I'm a bit stuck on how to say that $x\geq 0$. I could separate it into two clauses, and say $x=0$ or $x>0$, but then the issue becomes that I don't know how to express $x>0$ in this language.
A hint would be appreciated.
Hint. A real number $x$ is nonnegative if and only if it is a square of another real number.