An arithmetic progression has first term a a\,a and common difference bbb.
Prove that the sum of the first N N\,N terms of the progression is
SN=12N{2a+(N−1)b} S_N = \frac{1}{2}N\{2a + (N-1)b\} SN=21N{2a+(N−1)b}41 exam-style questions on WJEC A Level Maths 3.4.4 Sequences and Series (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.