Which of the following expressions correctly gives 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 expressions correctly gives 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}[a+(n-1)d]

(b)

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

(c)

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

(d)

S_n=a+(n-1)d