Circle Property (Angles in a segment)

Solution

Move Point A so that the red line passes 
through the end of the green line

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ZoomIn[-10.56,-2.71,9.94,10.89]

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α = 0.8203047484373349 rad (slider from 0 to 180*°, step 0.017453292519943295)
f = false
D = (-4.398838709677416, -2.048430107526882)
E = (4.010430107526881, -0.30302656546489715)
i = Segment(D, E)
j = LineBisector(D, E)
D' = Rotate(D, α / 2, E)
E' = Rotate(E, α / 2, E)
i' = Segment(D', E')
F = Intersect(j, i')
k = Circle(D, F, E)
G, H = Intersect(k, j)
p = CircumcircleArc(E, H, D)
A = (-5.9309677419354845, 5.097511068943705)
a = Segment(D, A)
D'_1 = Rotate(D, α, A)
b = Ray(A, D'_1)
β = Angle(D, A, D'_1)
c = 2.718281828459045
d = 2.718281828459045
e = 2.718281828459045
B = Intersect(a, b)
g = true
h = false