Using distance formula, the distance^2 from a,b to each of the points on the circle is the same ....
to 2,0 and 7,1 :
(a-2)^2 + (b-0)^2 = (a-7)^2 + (b-1)^2 simplify to
10a+2b = 46
to 2,0 and 3,5
( a-2)^2 + ( b-0)^2 = (a-3)^2 + (b-5)^2 simplify to
2a +10b = 30
Now you have two equations relating two unknowns....solve for a and b
Multiply top equation by -5 to get
-50a - 10 b = -230 and add it to the second equation to get
-48a = -200
a = 4.167. use this value of 'a' in one of the equatins to find b = 2.167