In an arithmetic sequence, the rrr-th term is given by ur=u1+(r−1)du_r = u_1 + (r-1)dur=u1+(r−1)d, where u1 u_1\,u1 is the first term and d d\,d is the common difference.
Show that the sum of the first n n\,n terms of the corresponding arithmetic series is
Sn=n2(2u1+(n−1)d) S_n = \frac{n}{2}(2u_1 + (n-1)d) Sn=2n(2u1+(n−1)d)36 exam-style questions on Edexcel A Level Maths 3.2 Arithmetic Series. Each one has a worked solution and a mark scheme showing where the marks go.