必须假定焦点在坐标轴上,否则条件不够.设椭圆的标准方程:x^2/a^2 + y^2/b^2 = 1 (,a > 0,b>0)
代入M,N的坐标:
3/a^2 + 1/(4b^2) = 1
1/a^2 + 3/(4a^2) = 1
a = 2,b =1
x^2/4 + y^2 = 1