The circle is symmetrical about a straight line, that is, the center of the circle is on this straight line. According to the chord length of the intersection of another straight line and the circle, the first relationship between A and B is obtained, and the second relationship between A and B is obtained. A and b can be solved simultaneously to get the equation of the circle.

The second problem is to set M (X 1, Y 1) and N (X2, Y2) by the method of setting without seeking, and then express x 1x2, y 1y2 by Vieta theorem, and then substitute it into x1x2+y66.