$設圓C:x²+y²+4x+2y-20=0 ，\;試求過原點的諸弦中點之軌跡.$

$α=%v$

O = (0, 0)
α = 0 rad (slider from 0 to 6.283185307179586, step 0.1*°)
a: y = tan(α) * x
A, B = Intersect(C, a)
b = Segment(A, B)
E = Midpoint(b)
Q = (-2, -1)