2.4 Quadratic formula and discriminant
Unit 2 · Quadratics
Ideas in this lesson
Use the quadratic formula
Identify a, b and c including their signs, then substitute into the formula.
Interpret the discriminant
b² − 4ac is positive for two distinct real roots, zero for one repeated real root, and negative for two nonreal roots.
Choose a solution method
The structure of the equation determines whether factoring, square roots or the formula is most efficient.
Derive the quadratic formula
Divide by the nonzero leading coefficient, complete the square and take both square roots.
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