(d)

Déplacer a pour étudier les différentes 
positions relatives des deux cercles

r = 2 (slider from 0 to 3, step 0.1)
r' = 3.2 (slider from 0 to 4, step 0.1)
a = -4.3 (slider from -7.5 to 7.5, step 0.1)
O = Point(a_1)
c = Circle(O, r)
O': (a, 0.0)
d = Circle(O', r')
texte2: "r + r' = " + (r + r')
texte3: "OO' = " + (abs(a))