Question 166148
since C(1,2) is the center if all lie on the circle then the distance between each point and C should be equal and would be the length of the radius.
distance between 2 points is {{{sqrt((change-in-x)^2+(change-in-y)^2)}}}
so distance between the following points and C are:

(-2,5)  {{{sqrt((-2-1)^2+(5-2)^2)}}}---->{{{sqrt(-3^2+3^2)}}}={{{3sqrt(2)}}}
(-2,-1) {{{sqrt((-2-1)^2+(-1-2)^2)}}}--->{{{sqrt(-3^2+-3^2)}}}={{{3sqrt(2)}}}
(4,-1)  {{{sqrt((4-1)^2+(-1-2)^2)}}}---->{{{sqrt(3^2+-3^2)}}}={{{3sqrt(2)}}}

they all lie on the circle with a radius of {{{3sqrt(2)}}}