This exam tips covers Substitution: Common Mistakes to Avoid within Simplifying Expressions for GCSE Mathematics. Revise Simplifying Expressions in Algebra for GCSE Mathematics with 11 exam-style questions and 5 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 14 of 19 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Substitution: Common Mistakes to Avoid
✗ (−3)² = −9
✓ (−3)² = (−3)×(−3) = 9
Negative × negative = positive!
✗ 2x² when x=3 gives 6² = 36
✓ 2(3²) = 2(9) = 18
Square the x first, then multiply by 2
✗ Forgetting BIDMAS
✓ Do powers before multiplication
x² + 3x: do x² first, then 3x, then add
✗ −3² = 9
✓ −3² = −(3²) = −9
Without brackets, the minus stays separate
Practice questions for Simplifying Expressions
Which two terms are like terms?
Explain why 3x + 2x² cannot be simplified to 5x³.
Quick recall flashcards
Substitution
Replace each letter with its given value, then calculate
Like Terms
Terms with same letter and power: 2x and 5x are like terms