Let F1 and F2 be fixed points, | F1F2 | = 6, and the moving point m satisfy | MF1 | + | MF2 | = 6, then the trajectory of the moving point m is () A. Ellipse B. straight line C. circle D. line segment

Let F1 and F2 be fixed points, | F1F2 | = 6, and the moving point m satisfy | MF1 | + | MF2 | = 6, then the trajectory of the moving point m is () A. Ellipse B. straight line C. circle D. line segment

In the plane, if the sum of the distances between the moving point m and the two points F1 and F2 is equal to 6, and 6 is just equal to the distance between the two points F1 and F2, then the trajectory of the moving point m is a line segment with F1 and F2 as the end points

If F1 and F2 are fixed points, | F1F2 | = 8, and the moving point m satisfies | MF1 | + | MF2 | = 8, then the trajectory of point m is? A ellipse B straight line C circle D line segment

|MF1|＋|MF2|=|F1F2|
If M is not on line F1F2
Then mf1f2 is a triangle, but this does not conform to the fact that the sum of the two sides is greater than the third side
So the three points are collinear
If M is not on F1F2
It is obvious that | MF1 | + | MF2 | > F1F2
So m is on line F1F2
Choose D