Answer:
The discriminant of a quadratic equation determines the nature of its roots. If the discriminant is negative, the quadratic equation has no real roots.
Therefore, the correct answers are:
2x^2 + x – 4 = 0
2 x^2 – 5 x – 3 = 0
3x^2 – 2 x + 4 = 0
–x^2 + x – 3 = 0