r = 1.501 (slider from 0.0010 to 8, step 0.01)
a = Segment((0.0, -4.0), (0.0, 4.0))
b = Segment((0.0, 0.0), (r, 0.0))
c = Circle((r, 0.0), r)
c' = Circle((r, 0.0), r)
d = Circle((r, 0.0), (0.0, 4.0))
texto1: "Área de la corona" + "
 = " + (Area[d]) + "- " + (Area[c]) + "
 = " + (Area[d] - Area[c])