l=2πr

\alpha

α = 0 rad (slider from 0 to 2.618, step 0.017453292519943295)
β: 75 ° - α
k: tan(β)
a: y = k x
D = Intersect(c, a, 2)
S = Intersect(d, a, 2)
e = Circle(S, 5)
A_1 = (3.105828541230249, 11.59110991546882)
A_2 = (3.105828541230249, -11.59110991546882)
O = (0, 0)
f = CircleArc(O, A_2, A_1)
s = Segment(O, A_1)
g = Segment(O, A_2)
γ: α 12 / 5
A = Rotate(D, -180 γ / π, S)
B = Rotate(D, -γ, S)
δ = Angle(B, S, D)
r = Segment(S, B)
C = If(α < 5 π / 6, (300, 300), (7, 0))
ε = Angle(A_2, O, A_1)