číslo kroku

A_{1} = (7, -4.18)
B = (21.02, -4.18)
p = Line(A_{1}, B)
T = Point(p)
g = OrthogonalLine(T, p)
S = Point(g)
k = Circle(S, T)
S_1 = Point(g)
k_1 = Circle(S_1, T)
a = 0 (slider from 0 to 2, step 1)