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 .