Answer:
(x-3)² + (y+2)² = 72
Explanation:
center is halfway between (9,-4) and (-3,8).
average of x-coordinates = (9-3)/2 = 3
average of y-coordinates = (-4+8)/2 = -2
center: (3,-2)
length of diameter = √[(9-(-3))²+(-4-8)²] = √288 = 12√2
radius = 6√2
(x-3)² + (y+2)² = (6√2)² = 72