O: (0, 0)
c = Circle(O, 1)
A: (1, 0)
n = 8 (slider from 1 to 20, step 1)
l1 = Sequence((cos((k * (2 * π / n))), sin((((k * 2) * π)) / n)), k, 1, n, 1)
polígono1 = Polygon(l1)
B: l1(1)
l2 = Sequence(Segment[A, l1(k)], k, 1, n - 1, 1)
a = Product(l2(k), k, 1, n - 1)