IGCSE Maths / Sequences and series
Finding a and d from two terms
Edexcel International GCSE Maths (4MA1), chapter 9: Sequences and series, specification point 3.1a. Part of the full course.
Read the revision notes · IGCSE Maths past papers
An arithmetic sequence can be rebuilt from two known terms by finding the common difference, d, and the first term, a. The key is that the nth term is a + (n − 1)d, because reaching term n takes n − 1 jumps.