Circle of radius 4 passes through O and points A(−3a, 0), B(0, −2b).
Let center be C(h, k) on circle: h2+k2=16.
Since A, B lie on circle: 3a2+23ah+h2+k2=16 gives h=−23a
And h2+2b+22bk+k2=16 gives k=−22b
Centroid G = (3−3a,3−2b). Setting x=3−3a and y=3−2b:
a=3x2 and b=29y2
From h2+k2=16: 43a+42b=16 → 3a+2b=64
Substituting: 9x2+9y2=64 → x2+y2=964
Radius = 38