Question

What is the equation of a circle that has a diameter with endpoints (3, -2) and (-7, 8)?

Answer 1

The center is the midpoint of the given diameter,
  ((3, -2) +(-7, 8))/2 = (-2, 3)

The radius is the distance from that to either end,
  √(5^2 +5^2) = 5√2

In standard form, the circle's equation is
  (x +2)² +(y -3)² = 50