If the discriminant is greater than zero then ...........

If the discriminant is greater than 0, then you should have two unique roots for the quadratic equation, which can both be positive or negative, or one positive one negative.

This is easily seen as, if you let n = the discriminant, then the quadratic formula becomes x = (-b +- sqrt(n))/2a; and if sqrt(n) > 0, which we know is true, then there will be two unique values of x.