A is any point on the circle, AM=6.
N (2 2,0), the distance from any point on the middle vertical line of line segment AN to both ends is equal, and the intersection point MA is at point P. 。
There is PN=PA
And am = pa+pm = 6;; That is, PM+PN=6.
That is to say, the sum of the distances from the moving point P to the two fixed points M and N is a constant of 6; According to the definition of ellipse, the parameters in ellipse
2a=6,a=3,
The focal length 2c=4, c=2,
So b=√(3? -2? )=√5
Elliptic equation: x? /9+y? /5= 1