First, find the midpoint of any two sides of AB, BC and CA (by the midpoint formula),

And the linear equations of these two sides (k value is obtained by two points and undetermined coefficient method),

Then the two midpoints are taken as a vertical line (obtained by two mutually perpendicular lines: k 1× k2 =- 1),

Two lines must intersect at the same point (get two vertical equations, form equations and solve them),

This intersection is the center of the circle.