What can I say about the roots of a quadratic equation without actually calculating them?

If a quadratic equation is of the form ax²+bx+c, calculate D (Discriminant) whose value is b²-4ac. 

If the value of D is negative, the equation has imaginary roots.

If the value of D is positive, the equation has real and distinct roots.

If the value of D is zero, the equation has real and equal roots.