What is the Discriminant? In a quadratic equation, the discriminant helps tell you the number of real solutions to a quadratic equation.In the quadratic formula you take the square root of the discriminant. This is not possible in real numbers when the discriminant is a negative number. Students will calculate the discriminant of quadratic equations and determine the number and type of solutions. Students will practice using the discriminant to determine the number of real solutions for a quadratic equations. Learn how to determine the discriminant of quadratic equations. Discriminant: the expression, b 2 − 4 a c , that is under the radical in the quadratic formula. The discriminant (b squared minus 4ac) under the radical sign in the formula determines the nature of the roots (real or imaginary). The discriminant of a quadratic formula is the part of the quadratic formula that determines the root type in a quadratic equation (imaginary, real, singular).