sum = 6 (slider from 0 to 8, step 0.1)
A = (2, 0)
B: -(A)
D = Point(Circle[B, sum])
sumK = Segment(B, D)
a = Segment(A, D)
b = LineBisector(a)
C = Intersect(b, sumK)
poly1, c, a_1, d = Polygon(A, D, C)