On 31 July 1589, the French king Henri III was killed by the monk Jacques Cl´ement
and was succeeded on the throne by Henri IV. In 1591, Fran¸cois Vi`ete, “one of the most
influential men at the court” of Henri IV [42, p. 3] published this very nice formula about
his problem XVIII, fourth book of Zetetica [41, p. 75] [42, p. 146]: