Determine the value of cos(20∘)cos(40∘)cos(80∘)\cos(20^\circ) \cos(40^\circ) \cos(80^\circ)cos(20∘)cos(40∘)cos(80∘).
1/81/81/8
1/41/41/4
3/8\sqrt{3}/83/8
3/4\sqrt{3}/43/4