B2 4ac. This excellent video shows you a clean blackboard with the instructors voice showing exactly what to do. And the types of root the equation has can be worked out as follows.
Calculate the discriminant using the formula.
When the value of the discriminant is zero then the equation will have only one root or solution. Combine all of the like terms and move them to one side of the equation. You need to take the numbers the represent a b and c and insert them into the equation. This information is helpful because it serves as a double check when solving quadratic equations by any of the four methods factoring completing the square using square roots and using the quadratic formula.