Pure · Sequences & series
Chapter 1 · 3
The idea
Arithmetic sequences and series
Sequences with a constant common difference — the nth-term rule and the sum formula, and where each comes from.
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Pure · Sequences & series
Arithmetic sequences and series
Sequences with a constant common difference — the nth-term rule and the sum formula, and where each comes from.
Why it works
Same step, every time
A cinema has seats in row 1, and every row back adds more seats. How many seats are in row 20? You could count row by row — or you could notice the pattern: a fixed start, and the same step repeated. Sequences like this are everywhere (seat rows, savings plans, stacking pipes), and this lesson builds the two formulae that answer every question about them: *what is the th term? and what do the first terms add up to?*Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
Start freeTakes a minute — no card.