Algebra
The discriminant
Positive for two real roots, zero for one repeated root, negative for none. Compute it before anything else.
The Formula
D = b^2 - 4ac
Positive for two real roots, zero for one repeated root, negative for none. Compute it before anything else.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| D | Discriminant | squared units of b | Its square root is the distance from the vertex to each root, scaled by a. |
What Each Symbol Means
Dsquared units of b
Discriminant
Its square root is the distance from the vertex to each root, scaled by a.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to solve a quadratic equation page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Solve A Quadratic Equation, filed under Math. Every number the guide produces comes from substituting into this one line.