ION PĂTRAŞCU 1, CĂTĂLIN I. BARBU 2 1. “Fraţii Buzeşti” National College, Department of Mathematics, Ion Cantacuzino 15, 200818 Craiova, Romania, e-mail: patrascu_ion@yahoo.com
2. “Vasile Alecsandri” National College, Department of Mathematics, Vasile Alecsandri 37, 600011 Bacău, Romania, e-mail: kafka_mate@yahoo.com