if b^2 - 4ac < 0 then you have two imaginary solutions
if b^2 - 4ac = 0 then you have 1 real solution
if b^2 - 4ac > 0 then you have 2 real solutions
for example, for x^2 + 5x + 9, a = 1, b = 5 and c = 9
b^2 - 4ac = (5)^2 - 4(1)(9) = 25 - 36 = -11, so you have two imaginary solutions.