焦点为F1(0,-6),F2（0,6）,
c=6,焦点在y轴
y^2/b^2-x^2/a^2=1
a^2+b^2=c^2
b^2=36-a^2
把M代入
25/(36-a^2)-4/a^2=1
25a^2-4(36-a^2)=a^2(36-a^2)
a^4-7a^2-144=0
(a^2-16)(a^2+9)=0
a^2>0
a^2=16
b^2=20
所以y^2/20-x^2/16=1