This exam tips covers Common Mistakes to Avoid within Surds for GCSE Mathematics. Revise Surds in Number for GCSE Mathematics with 14 exam-style questions and 22 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 13 of 14 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 13 of 14
Practice
14 questions
Recall
22 flashcards
Common Mistakes to Avoid
❌ Wrong: √a + √b = √(a+b)
✅ Right: Cannot combine different surds
√9 + √16 = 3 + 4 = 7, NOT √25 = 5
❌ Wrong: √18 = 9√2
✅ Right: √18 = 3√2
√18 = √(9×2) = 3√2 (take square ROOT of 9)
❌ Wrong: 3√2 × 2√3 = 5√5
✅ Right: 3√2 × 2√3 = 6√6
Multiply coefficients AND surds: 3×2=6, √2×√3=√6
❌ Wrong: Leaving denominator with surd
✅ Right: Always rationalize
1/√2 should be written as √2/2