Which of these functions is surjective but not injective on R\mathbb{R}R?
f(x)=x3−xf(x) = x^3 - xf(x)=x3−x
f(x)=exf(x) = e^xf(x)=ex
f(x)=x2f(x) = x^2f(x)=x2
f(x)=tan(x)f(x) = \tan(x)f(x)=tan(x)