Here's the problem:
from sympy import symbols, Plot
from sympy.geometry import *
c1 = Circle(Point(0,0),2)
a = Point(3,0)
at = c1.tangent_lines(a)
DomainError: can't compute a Groebner basis over RR
A little web search indicates that this was a problem with older versions of sympy, but Sage includes a newer version for which this issue is not supposed to be a problem. Any ideas on how to get round this?
