Paper 1 · Algebra
⏱ Tested in 5+ recent exam questions
Lesson 11 of 23
Algebra 11 – Solving cubic equations
You’ll learn
- Find a first root of a cubic by trial and error (x = 1, −1, 2, −2, …)
- Convert the root to a factor and divide it out by polynomial long division
- Factorise the remaining quadratic to read off all three roots
- Handle non-monic cubics whose factors give fractional roots like x = ½
Formula used
Roots of the quadratic equation
x = (-b ± √(b² − 4ac)) / 2a
On page 20 of the log tables — read it off, don’t memorise.Most recent exam questions
- 2025 P1 Q1(c)
- 2024 P1 Q7(b)(i) — deferred
- 2024 P1 Q7(b)(ii) — deferred
- 2023 P1 Q4(b)(i) — deferred
- 2023 P1 Q4(b)(ii) — deferred
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