Which function is its own inverse?
f(x)=exf(x) = e^xf(x)=ex
f(x)=x3f(x) = x^3f(x)=x3
f(x)=1/xf(x) = 1/xf(x)=1/x
f(x)=2xf(x) = 2xf(x)=2x