a = 0 (slider from -5 to 5, step 0.1)
b = 0 (slider from -5 to 5, step 0.1)
r_1 = 5 (slider from 0 to 5, step 0.1)
c: (x - a)^(2) + (y - b)^(2) = r_1^(2)
C = Center(c)
A = Point(c)
r = Segment(C, A)