číslo kroku

A_{1} = (7, -4.18)
B = (21.02, -4.18)
f = Line(A_{1}, B)
A = Point(f)
g = OrthogonalLine(A, f)
S = Point(g)
c = Circle(S, A)
S_1 = Point(g)
d = Circle(S_1, A)
a = 0 (slider from 0 to 2, step 1)