Quadratic Equation Question

Given that a quadratic equation does not have roots on the x - axis, which condition must be true?

a) b^2 - 4ac < 0
b) b^2 - 4ac = 0
c) b^2 - 4ac > 0

Help please!

a) (b^2 - 4ac) < 0
when you sqrt it (for the quadratic formula) you will get a sqrt of a negative number, which is not possible.
Until you get to later maths, where i is introduced.

a) b^2 - 4ac < 0

d = b^2 - 4ab
when d < 0, quadratic equation does not have real roots.