Thank you..
I'll try to give you some guidance,
the definition of one-to-one is:
$\displaystyle \forall x,y \in \mathbb{R} f(x)=f(y) \implies x = y $
and onto:
$\displaystyle \forall y \in \mathbb{R} \exists x \in \mathbb{R} f(x) = y$.
Also to prove that something is not one to one you need to find $\displaystyle x,y\in \mathbb{R}$ such that $\displaystyle f(x) = f(y)$ and $\displaystyle x \neq y$.
Hope that helps.