The discriminant is the part of the quadratic formula underneath the square root symbol: b²-4ac. The formula derives from the quadratic formula.The discriminant won't tell you what the roots or Solutions of your quadratic equation are but they will tell you what kind of roots they are. This formula is used to find out whether the roots of the quadratic equation are real or imaginary. Steps for Finding the Discriminant of a Quadratic Equation. Step 1: Identify the values of a, b, and c in the quadratic equation. To calculate the discriminant of a quadratic equation, the formula is b2 – 4ac. To find the discriminant of a quadratic equation, we calculate D = b 2 − 4 a c . 1) Find the discriminant of each quadratic equation. B2 = 9 and 4ac = 20.