A = (-0.9, 0.56)
B = Point(Circle[A, 4.9])
c = Segment(A, B)
B' = Rotate(B, (-(78°)), A)
α = Angle(B', A, B)
b = Ray(A, B')
d = Circle(A, 7.8)
C = Intersect(d, b)
a = Segment(B, C)