Y2/4-x2/12=1
x2/9+y2/25=1
化为：
y^2-x^2/3=4.(1)
25x^2/9+y^2=25.(2)
(2)-(1)得：
28x^2/9=21
x^2=27/4
y^2=4+x^2/3=4+9/4=25/4
x=±3√3/2
y=±5/2