Paper 1 · Algebra ⏱ Tested in 5+ recent exam questions Lesson 15 of 22

LCOL Algebra 15: Using the -b Formula to solve Quadratic Equations

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In this lesson you’ll learn to

  • Use the −b formula to solve quadratics that won’t factorise
  • Identify a, b and c with their signs; give answers to 2 d.p. or in surd form

Formula used

The −b (quadratic) formula

x = (−b ± √(b² − 4ac)) / 2a

On page 20 of the log tables — read it off, don’t memorise.

Most recent exam questions

  • 2025 P1 Q5(b) — main sitting
  • 2024 P1 Q3(b) — main sitting
  • 2023 P1 Q6(c) — main sitting
  • 2021 P1 Q3(c) — main sitting
  • 2018 P1 Q3(a) — main sitting
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