Question 1084215
Need to know the center and the radius.
Midpoint of diameter is center, which is midpoint formula, which gives (-1, 1) and the radius is the distance from the center to either end of the diameter.  That is the distance formula, sqrt ((x2-x1)^2+(y2-y1)^2)= sqrt (16+16)=sqrt (32)
so r^2=32.  The equation of a circle is x^2+y^2=r^2.  So once one has the sqrt of the radius (here sqrt (32)), it has to be squared (32) to be part of the equation.  
(x+1)^2+(y-1)^2=32
K.