4x^2+9y^2=36
x^2/9+y^2/4=1
a^2=9,b^2=4
所以c^2=5
所以所求椭圆c^2=5
e=c/a
a=c/e
所以a^2=c^2/e^2=5/(1/5)=25
b^2=a^2-c^2=20
所以x^2/25+y^2/20=1