State the correct expression for the sum of the first terms of an arithmetic…

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

Problem

State the correct expression for the sum

S_n

of the first

n

terms of an arithmetic progression with first term

a

and common difference

d

. (a)

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

(b)

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

(c)

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

(d)

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