MF2 is multiplied by 1 and MF 1, which means that MF 1 is perpendicular to MF2, and the circle with the diameter of F 1F2 is in the ellipse, that is, 2c is smaller than 2b, that is, the square of c is smaller than 4b, that is, the square of a minus the square of c is smaller than 4 times, the root of c2 in a is 2, and the eccentricity is greater than 0.

2. calculate 2/2 b of cos2, which is equal to b divided by a, and then sort it out. I won't count.

3, F 1F2=2c, equilateral triangle bisects, that is, the midpoint is vertical (≈f 1mf 2, where m is the intersection point of ellipse bisection), then 2a=F 1M+F2M, 2c=F 1F2, and triangle f/kloc. The rest is easy to say.

4. Let me think again.

I'm not a teacher, I just finished studying here ~ but I promise I'm correct.