Consider the following statements about a quadratic $ax^2+bx+c=0$ with real coefficients: Which of the following is correct?

1. If $b^2-4ac > 0$, the roots are real
2. If $b^2-4ac < 0$, the roots are imaginary
3. If $b^2-4ac = 0$, the roots are real and equal

• ai and ii
• bii and iii
• ci and iii
• di, ii and iii