sum = 6.2 (slider from 0 to 8, step 0.1)
A = Point(xAxis)
B: -(A)
D = Point(Circle[B, sum])
sumK = Segment(B, D)
d = Line(B, D)
b = Segment(A, D)
a, c = AngularBisector(b, sumK)
A' = Mirror(A, a)