Radius is the distance between the center and any point on the circle.
r=distance =√((x2-x1)² +(y2-y1)²) =√((5-(-3))²+(-7-(-1))²)=√(64+36)=√100 = 10
r=√100
Equation of the circle , where (h, k) coordinates of the center of the radius.
(h,k)=(5,-7)
(x-h)² +(y-k)² = r²
(x-5)² +(y+7)² = (√100)²
(x-5)² +(y+7)² = 100