園的極線
Author: 藍邦偉  老師

移動圓心Q點及圓上一點D形成一圓，移動P點
(1) P在圓外:過P對圓作切線，切點為A,B，極線方程式為\line{AB}
(2) P在圓上:極線方程式即為切線方程式

圓的極線

u = Vector((x(Corner[1]), 0), (x(Corner[3]), 0))
v = Vector((0, y(Corner[1])), (0, y(Corner[3])))
Q = (2.12, 0.8)
D = (4, 2)
c = Circle(Q, D)
P = (7.04, 2.68)
a, b = Tangent(P, c)
A = Intersect(c, a)
B = Intersect(c, b)
e = Polar(P, c)