Quadratic formula and discriminant
The discriminant classifies the real solutions of a quadratic equation.
Key knowledge
For real coefficients with a≠0, completing the square gives the quadratic formula. D=b²−4ac is positive for two distinct real roots, zero for one repeated real root, and negative for no real roots.
Values and equations
D=b^2−4ac; x=(−b ± √D)/(2a)
- a, b, c
- Real coefficients, a≠0
- D
- Discriminant
- x
- Root; use complex square root when D<0
Conditions and scope
- The equation is ax²+bx+c=0 and coefficients are ordinary real numbers.
- For D<0, complex square roots give two nonreal conjugate roots; no rationality classification follows from D's sign alone.
Table 1 rationality labels are not valid for arbitrary real coefficients and are excluded.
Sources · 1
References
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Evidence and review
Checked the stated quadratic formula and discriminant and restrictions against the listed primary sections; exact inspected boundaries are in the author receipt.
2026-10-10 · Independent Physics and Measurement reference editor (AI editorial bounded review). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
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- foundation-math-quadratic-formula
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions