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Rearranging formulae requires students to change the subject of an equation, using the same inverse-operation skills as solving equations but with multiple variables. Higher-tier questions involve subjects that appear twice or under roots and powers.
Students make these errors again and again. Knowing them in advance gives you a head start.
Performing inverse operations in the wrong order
Forgetting to square both sides when the subject is under a square root
Not factorising when the new subject appears in multiple terms
Insights pulled from Cambridge IGCSE (0580) examiner reports — the exact mistakes candidates make every year.
You can ONLY cancel FACTORS (things multiplied), not terms added/subtracted. Factorise numerator and denominator first, then cancel matching brackets. Never cancel x² from x² − 25.
“Candidates who recognised that the numerator and denominator should be first factorised to create products were frequently successful. However, a common wrong approach was to merely cancel the x² in the first step with (x² − 25)/(x² − x − 20) = −25/(−x − 20) = 5/(x + 4), or similar, commonly seen.”
Source: CIE 0580 · November 2021 · Paper 4 · Q7a
In 'show that k = 8' questions, you must DERIVE 8, not assume it. Starting from 'k = 8' and working both ways is circular and scores zero. Work from the given info towards the target.
“This 'show that' question was often not attempted. Candidates who did attempt it often did not gain credit as they generally used the answer of k = 8 as part of their working. Candidates should be reminded that in any 'show that' question candidates must not use what they are asked to show as part of their answer.”
Source: CIE 0580 · November 2021 · Paper 3 · Q5
When raising a power to a power, MULTIPLY the exponents: (x³)³ = x⁹, not x⁶. But for coefficients like (4x³)³, the coefficient is raised: 4³ = 64, not 4 × 3 = 12.
“A small number incorrectly simplified the power by adding to give 6 rather than multiplying to give 9. Others correctly multiplied the powers but also multiplied the coefficient giving the incorrect answer of 12x⁹.”
Source: CIE 0580 · June 2024 · Paper 2 · Q21b
Based on 3of 510+ insights extracted from CIE 0580 examiner reports (2018–2024).
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