X^2/13^2+y^2/12^2=1a=13,b=12,c^2=a^2-b^2=25,c=5焦点坐标(-5,0),(+5,0)设M坐标(x,y)MF1:MF2=2:33MF1=2MF29MF1^2=4MF2^29[(x+5)^2+y^2]=4[(x-5)^2+y^2]化简得:x^2+26x+y^2+25=0