Which one of the following gives the sum of the first terms of an arithmetic…

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

Problem

Which one of the following gives the sum

S_n

of the first

n

terms of an arithmetic progression solely in terms of its first term

a

and

n

th term

a_n

? (a)

n(a+a_n)

(b)

\dfrac{n}{2}(a_n-a)

(c)

\dfrac{n}{2}(a+a_n)

(d)

\dfrac{a+a_n}{2}