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Answer:
(x -4)² +(y -2)² = 20
Explanation:
The circle is the circumcircle of triangle OAB. Then OA will be a diameter if angle OBA is a right angle. We can check that by looking at the slopes of AB and BA.
B-O = (6, 6)-(0, 0) = (6, 6) ⇒ slope = Δy/Δx = 6/6 = 1
A-B = (8, 4) -(6, 6) = (2, -2) ⇒ slope = -2/2 = -1
These slopes have a product of -1, so OB ⊥ BA. The hypotenuse (OA) of ΔOBA is the diameter of the circle.
Then the midpoint of the hypotenuse is the center of the circle.
C = (O +A)/2 = ((0, 0) +(8, 4))/2 = (4, 2)
The equation is ...
(x -h)² +(y -k)² = r² . . . . . circle with center (h, k) and radius r
The radius is the distance from O to C, so is ...
r² = 4² +2² = 20
and the equation of the circle is ...
(x -4)² +(y -2)² = 20 . . . . equation of the circle