r

a = 1 (slider from -6 to 6, step 0.1)
b = -2 (slider from -6 to 6, step 0.1)
r = 3 (slider from 0 to 6, step 0.1)
Eq1: (x - a)^(2) + (y - b)^(2) = r^(2)
S: (a, b)
A = Point(Eq1)
f = Segment(S, A)