A = (3, 0)
B = (1, 4)
χ = 1.7 (slider from -5 to 5, step 0.1)
M: (χ, 2.0 - 2.0 * χ)
πολύγ.1, a_1, b, m = Polygon(B, M, A)
α = Angle(A, M, B)