Question 1073399
HINT: Midpoint of the entire square
Another HINT:  Midpoint of any of the sides



Middle of OB same as CA
(0,2)
and this is the center of the circle.


Middle of segment BA
{{{x=(0+2)/2=1}}}
-
{{{y=(4+2)/2=3}}}
-
The point (1,3) is on the circle.



Distance From Center to (1,3) gives the radius.
r, radius
{{{r^2=(1-0)^2+(3-2)^2}}}
{{{r^2=1+1}}}
{{{r^2=2}}}



EQUATION
{{{(x-0)^2+(y-2)^2=1}}}
{{{highlight(x^2+(y-2)^2=1)}}}