In: Advanced Math
construct a bijective function of f:[0, inf) -> R
We are going to define a bijective function from
to
. At
first we define
. Then we
define the function interval-wise.
for all
and
.
Observe that image of (0,1] under f is (0,1] and image of (1,2] is
[-1,0). Similarly, we define
, and
. Again observe that image of (2,3] is (1,2] and image of (3,4] is
[-2,-1).
Again we define
and
. Then the images will be (2,3] and [-3,-2) respectively. In
general, we define
and
. Now it can be easily checked that
is a bijection. Infact, injectivity of this function is trivial
and for the surjectivity, let
.
If
, then
.
If y>0, then
for some
. Then
. If y<0, then
for some n. Then
. Hence
is
surjective.