Question 889557
More than one way to do this.  Look for the midpoint of any pair of opposite corners.  Use distance formula to find half the length of a diagonal.


A pair of opposite corners is (-1,-3) and (-9,5).


Center point should be at {{{x=(-1-9)/2=-4}}} and {{{y=(-3+5)/2=1}}}


Diagonal length, {{{sqrt((-1-(-9))^2+(-3-5)^2)}}}
{{{sqrt((8)^2+(-8)^2)}}}
{{{sqrt(128)}}}
{{{sqrt(64*2)}}}
{{{8*sqrt(2)}}}
HALF of that is {{{highlight_green(4*sqrt(2))}}}.  This is also the size of the radius of the circle.


Equation for the circle is {{{highlight((x+4)^2+(x-1)^2=(4sqrt(2))^2)}}}.