Which function is strictly increasing on R\mathbb{R}R?
f(x)=x3+xf(x) = x^3 + xf(x)=x3+x
f(x)=x2f(x) = x^2f(x)=x2
f(x)=sin(x)f(x) = \sin(x)f(x)=sin(x)
f(x)=1xf(x) = \frac{1}{x}f(x)=x1