Real Numbers — Quick Notes & Formula Sheet Class 10 CBSE Mathematics · Chapter 1 · Complete Revision Guide 1. Euclid's Division Lemma For any two positive integers a and b , there exist unique integers q (quotient) and r (remainder) such that: a = bq + r, where 0 ≤ r < b This is simply the everyday idea of division ("dividend = divisor × quotient + remainder"), but stated formally so it can be used to build an algorithm. ⚠ Trap: The remainder range Students often write 0 ≤ r ≤ b (with r allowed to equal b). This is wrong — r must be strictly less than b . If r equals b, the division isn't complete. 2. Euclid's Division Algorithm (to find HCF) To find HCF(a, b) where a > b, apply the lemma: a = bq + r If r = 0, then b is the HCF. Stop here. If r ≠ 0, apply the lemma again to the pair ...