ω = 0.9424777960769379 rad (slider from 0 to 180°, step 0.5°)
β = 3 (slider from 0 to 15, step 1)
Α = (-2.82, 1.76)
Γ = Point(Circle[Α, β])
b = Segment(Α, Γ)
Β' = Rotate(Γ, ω, Α)
c = Ray(Α, Β')
d = OrthogonalLine(Γ, b)
εϕω: tan(ω)
Α' = Rotate(Α, (-ω), Γ)
AΓΒ = Angle(Α', Γ, Α)
a = Ray(Γ, Α')
e = OrthogonalLine(Α, b)
Β = Intersect(e, a)
f = Segment(Α, Β)
g = Segment(Β, Γ)
φ = Angle(Α, Β, Γ)