Quadratics
Lesson 2 of 14
Standard practice
The quadratic formula
Objective. Solve any quadratic using x = (−b ± √(b² − 4ac)) / 2a.
- 1. Learn
- 2. Worked example
- 3. Practice
- 4. Feedback
- 5. Continue
Learn: the key idea
The formula always works. The discriminant b² − 4ac tells you how many real roots exist before you solve.
Worked example
Solve 2x² + 3x − 4 = 0 to 2 d.p.
- 1a = 2, b = 3, c = −4.
- 2b² − 4ac = 9 + 32 = 41.
- 3x = (−3 ± √41) / 4.
Answer: x = 0.85 or x = −2.35
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