Arithmetic Progressions

This chapter introduces arithmetic progressions (APs) — lists of numbers in which each term differs from the previous one by a fixed common difference. It covers identifying an AP and its first term and common difference, the formula for the nth term $a_n = a + (n-1)d$, the sum of the first n terms $S_n = \frac{n}{2}[2a + (n-1)d]$, the arithmetic mean, selecting terms in AP, and a wide range of real-life word problems. It is a high-scoring, formula-driven chapter important for both CBSE and State Board examinations.