How to do problem 1516 Find a function f R rightarrow R tha

How to do problem 15.16 ?

Find a function f: R rightarrow R^+ that is one-to-one.

f(x)=x is one to one function

Because for every value of x in domain has unique distinct image in range.

Here domain R is given but codomain is R+

Hence some of the elements of domain are left out in order to satisfy one to one function specification