The Discriminant
Overview
Before solving a quadratic, you can already tell how many real solutions it has, just from a single number buried inside the formula. That number is the discriminant, \(b^2-4ac\), and reading its sign is one of the quickest, most powerful checks in algebra.
In this lesson you will learn what the discriminant reveals about the roots of a quadratic: two distinct roots, one repeated root, or none at all. You will then use it to answer a favourite exam question, deciding whether a straight line cuts, touches or misses a curve, all without solving the equation fully.
Objectives
- Know the conditions for a quadratic equation to have two real roots, two equal roots or no real roots, using the discriminant.
- Use the related conditions for a given line to intersect, be a tangent to, or not intersect a given curve.
Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on The Discriminant. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- What is the discriminant of a quadratic ax^2 + bx + c = 0? A. b^2 + 4ac B. b^2 - 4ac C. 4ac - b^2 D. b - 4ac Answer: B
- If b^2 - 4ac > 0, the quadratic has: A. no real roots B. one repeated root C. two distinct real roots D. infinitely many roots Answer: C
- How many real roots has 2x^2 + 3x + 5 = 0? A. 0 B. 1 C. 2 D. 3 Answer: A
- The equation x^2 - 6x + 9 = 0 has a discriminant of: A. 72 B. 36 C. 0 D. -36 Answer: C
- y = x + k is a tangent to y = x^2 when k equals: A. 1/4 B. -1/4 C. 0 D. -1 Answer: B
Available on the Green Bridge App
Download the Green Bridge CBT app on your phone or computer to access full lesson notes, practice questions, and more.
Available on the Green Bridge App
Download the Green Bridge CBT app on your phone or computer to access full lesson notes, practice questions, and more.
Recommended Books
Practice Mock Questions
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