The equation is
.
The equation tells us to take an input
and squaring.
For any input of
, we get only one output for
.
An input
.
Substitute
in
.
.
An input
.
Substitute
in
.
.
For any input of
, we get only one output for
.
So, the equation
defines
as a function of
.
The equation
defines
as a function of
.