esercizi x2 + 5x - 36 = 0          -5 [52 - 4·1·(-36)] x1,2 = ----------------------                   2          -5 (25+144) x1,2 = ----------------------                   2          -5 169 x1,2 = ----------------               2          -5 13 x1,2 = ------------               2 x1 = 4 x2 = -9