for his work on ribonucleaseandfor their contribution to the understanding of the connection between chemical structure and catalytic activity of the ribonuclease molecule
for their elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphateandfor his discovery of an ion-transporting enzyme, Na+, K+ -ATPase
... which are real. (Geometrically, this means that the parabola intersects the x-axis in two points.)
If the discriminant is negative, then there are two different solutions ...