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.

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