The area of the circle with radius
is
.
The radius
is always positive and greater than zero.
The area of the circle appears to be continuous in the interval
.

Apply derivative on each side with respect to
.

on
.
Therefore, the function is one-to-one and is strictly monotonic over the interval.
\Inverse exists.
\Find the inverse of the function.
\The function is
.
Rewrite the function as
.
Interchange the variables
and
.



Substitute
.
The inverse of the function is
.
The function has inverse function.
\The inverse of area of the circle is
.