1.8-1 
system:sage


{{{id=1|
x=var('x')
a=3 #LET US SUPPOSE
e=2/a
b=sqrt(a^2*(1-e^2))
y=sqrt(b^2*(1-x^2/a^2))
plot(y,(x,-a,a),color="blue")+plot(-y,(x,-a,a),color="blue")
///
<html><font color='black'><img src='cell://sage0.png'></font></html>
}}}

{{{id=2|

///
}}}

{{{id=3|

///
}}}