λ = -1 (slider from -10 to 10, step 0.1)
a: (2.0 * λ + 1.0) * x - 3.0 * λ * y - 2.0 = 0.0
b: 3.0 * λ * x + (λ + 2.0) * y + 1.0 = 0.0
A = Intersect(a, b)
B = Point(a)
C = Point(b)
α = Angle(C, A, B)
β = Angle(B, A, C)