What is the discriminant in a math equation?

In a quadratic equation of the form ax2+bx + c = 0, the discriminant is b2-4ac.

It determines the nature of the roots of the equation. If it is positive, there are two real roots; if is negative, there are two complex roots; if it is zero, there is one real root, often called a double root. Both real roots are rational if and only the discriminant is a perfect square.