D'Aulísio, Marli de Bem Gomes, et al. “ The Distribution of Points of Maximum or Minimum of Second Degree Regression Equations ”. Anais Da Escola Superior De Agricultura Luiz De Queiroz, vol. 33, Jan. 1976, pp. 291-07, https://doi.org/10.1590/S0071-12761976000100026.