Which of the following is the correct formula for the sum of the first terms of an…

MATHEMATICS · Single correct · A Level · Mathematics · Sequences and series · Sequences and series

Problem

Which of the following is the correct formula for the sum

S_n

of the first

n

terms of an arithmetic progression whose first term is

a

and common difference is

d

? (a)

S_n = n\,[2a + (n-1)d]

(b)

S_n = \dfrac{n}{2}\,[2a + (n-1)d]

(c)

S_n = \dfrac{n}{2}\,[2d + (n-1)a]

(d)

S_n = \dfrac{n}{2}\,[a + nd]