∡(ACB)

v-u

∡(u,v)

c_2

C = (0, 0)
A = (5, 1)
B = (1, 4)
d1, b, c, a = Polygon(C, A, B)
γ = Angle(A, C, B)
u = Vector(C, A)
v = Vector(C, B)
w = Vector(A, B)
α = Angle(A, C, B)
f = OrthogonalLine(C, c)
F = Intersect(f, c)
ε = Angle(A, C, F)
δ = Angle(F, C, B)
c_1 = Segment(B, F)
g = Segment(F, A)
h = Segment(C, F)
D = (3.3081818181818186, -2.2081818181818162)
E = (4.853636363636368, -2.2081818181818162)