Question 433280
The largest circular garden that will fit in a 20x20 square is one with a diameter of 20.  Radius is half the diameter, so the radius is 10.
Area of a circle is {{{pi*r^2}}} = {{{pi*10^2=100pi=314.15ft^2}}}
Area of the backyard is 20x20=400.
The area of the yard that is not in the garden would be the area of the square minus the area of the circle.
{{{400-314.15=83.85ft^2}}}