From am = λ MB, (x-a, y)=λ(-x, b-y),

x？ a=？ λxy=λ(b？ Y), so that a = (1+λ) XB = (1+λ) λ y,

From a2+b2=25, X225 (1+λ) 2+Y225 λ 2 (1+λ) 2 =1.

① If λ= 1, the equation is x2+y2 = 254, and the trajectory is a circle;

(2) If 0 < λ < 1, the trajectory e is expressed as an ellipse with the focus on the X axis;

(3) If λ > 1, the trajectory e represents an ellipse whose focus is on the y axis.

(2) When λ = 23, the trajectory equation is X29+Y24 = 1,

Let C(x 1, y 1), D(x2, y2),

Let the slope of the chord CD be k, and replace the difference with it, so:

x 12？ x229-y 12？ y224=0，

From x 1+x2=2, y 1+y2=2, k=-49,

The equation of ∴ straight line CD is y- 1=-49(x- 1), and 4x+9y- 13 = 0 after sorting.