A double root occurs when a second-degree polynomial touches the x-axis but does not cross it. Both ends of the parabola extend up or down from the double root on the x-axis.
A double root can be confirmed mathematically by examining the equation for solving a second-degree polynomial. If the discriminant, or square root of b^2-4*a*c, is equal to zero, then the equation has a double root. Finishing calculating the solution of the equation will yield two answers of the exact same magnitude. Other possible solutions for a polynomial equation include having two roots with two x-axis intersections, or no roots if it doesn't cross the x-axis.