Given the two end of the diameter of the circle, we are able to compute the center of the circle as 0.5*[(-1,3)+(7,-7)]=(3,-2). The radius of the circle is 0.5*sqrt[(-1-7)^2+(3+7)^2]=sqrt(41). Therefore the equation of the circle is (x-3)^2+(y+2)^2=41.