Determining the Nature of the Roots of a Quadratic (Discriminant)

Calculate the discriminant $b^2-4ac$ for a given quadratic and state whether it is positive, negative, or zero.

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Learning objective overview

Master Teaching Guide coverage for this objective.

Current NZC (2007)
  • NA6-5
New NZC (2026)
  • NZC26-P4-ALG-ER-K-Y10-02
  • NZC26-P4-ALG-ER-K-Y10-04
  • NZC26-P4-ALG-ER-P-Y10-09

Resources

  • No external resource is currently specified.

Terminology

  • Discriminant
  • Real distinct roots
  • Repeated root
  • No real roots
  • x-intercepts

Task goals

  • Foundation: Calculate the discriminant $b^2-4ac$ for a given quadratic and state whether it is positive, negative, or zero.
  • Proficient: Use the sign of the discriminant to classify the roots as two real distinct roots, one repeated real root, or no real roots, and relate this to the number of x-intercepts on the parabola.
  • Excellence: Find the value(s) of an unknown coefficient or constant so that a quadratic has a specified nature of roots (e.g. equal roots or no real roots), justifying the answer using the discriminant.

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Determining the Nature of the Roots of a Quadratic (Discriminant)

Determining the Nature of the Roots of a Quadratic (Discriminant)

Know

Any positive real number has two square roots: one positive (the principal square root) and one negative (e.g. for 16, 4 and −4).

Statement▸
Year 10 · Algebra · Equations and relationships
NZC26-P4-ALG-ER-K-Y10-02
Know

There are 0, 1, or 2 real-number solutions to x^2 = a, where a is a number.

Statement▸
Year 10 · Algebra · Equations and relationships
NZC26-P4-ALG-ER-K-Y10-04

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