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The radius of the circle having centre at (2,1) whose one chord is the diameter of the circle x2 +y2 -2x-6y+6=0
thus the radius of the smaller given circle is 2 and its centre is (1,3).
distance b/w the two centres = (1+4)1/2 = 51/2
thus the radius of required circle = (5 + 4)1/2 = 3.