Home Courses QCE Year 11 Maths C Arithmetic Sequences and Arithmetic Series (Free) Set up a Sum Formula ← Previous Topic Next Topic → TopicSet up a Sum Formula Topic Progress: The sum of n terms of an arithmetic sequence with a as its first term and l as its last term is given by \( \ \displaystyle{S}_{n} = \frac{n}{2}({a} + \ell) \).Practice Questions Show Solution Show Solution Show Solution Show Solution Show Solution Show Solution Show Solution Show Solution Show Solution Back to Lesson