应增加中心在原点的条件,
设椭圆方程为：x^2/a^2+y^2/b^2=1,
12/a^2+1/b^2=1,(1)
3/a^2+4/b^2=1,(2)
(2)*4-(1)式,
15/b^2=3,
b^2=5,
a^2=15,
则方程为：x^2/15+y^2/5=1.