Which function is bijective on R\mathbb{R}R?
f(x)=x2f(x) = x^2f(x)=x2
f(x)=∣x∣f(x) = |x|f(x)=∣x∣
f(x)=x3f(x) = x^3f(x)=x3
f(x)=sin(x)f(x) = \sin(x)f(x)=sin(x)