Question 328504
Let a circle side be x.

Since the sides are all the same length, we have 

{{{x^2+x^2=36}}}

{{{2x^2=36}}}

{{{x^2=18}}}

{{{x=3*sqrt(2)}}}

Since this is a side length, the circle's radius is half that.

The area of a circle is {{{(pi)*r^2}}} with {{{r=3*sqrt(2)/2}}}

area of circle: {{{(pi)*(3*sqrt(2)/2)^2=9*(pi)/2}}}

As an added bonus, the area of the square is 18.

the ratio of the square area to the circle area is {{{18/(9*(pi)/2)=4/(pi)}}}

This is true in general.