S1

A = (16.132006883619578, -5.91782306220951)
B = (10.30662973880129, 3.594658338191548)
A' = Rotate(A, 45*°, B)
a = Line(A, B)
b = Line(A', B)
C = (5.7731352974894135, -2.7616798034496597)
D = (4.8, -1.54)
E = (2.18, -2.96)
Vieleck1, e, c, d = Polygon(C, D, E)
C' = Mirror(C, a)
D' = Mirror(D, a)
E' = Mirror(E, a)
Vieleck1', e', c', d' = Polygon(C', D', E')
E'' = Mirror(E', b)
C'' = Mirror(C', b)
d'' = Segment(E'', C'')
D'' = Mirror(D', b)
D''_1 = Mirror(D', b)
E''_1 = Mirror(E', b)
c'' = Segment(D''_1, E''_1)
C''_1 = Mirror(C', b)
C''_2 = Mirror(C', b)
C''_3 = Mirror(C', b)
D''_2 = Mirror(D', b)
e'' = Segment(C''_3, D''_2)
f = Line(C'', D'')
g = OrthogonalLine(C, f)
α = Angle(a, b)
F = Intersect(f, g)
η = Angle(C, F, D'')