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

MATHEMATICS · Single correct · CBSE · Mathematics · Arithmetic Progressions · Arithmetic Progressions

Problem

Which of the following expressions gives the sum

S_n

of the first

n

terms of an arithmetic progression when only the first term

a

and the last term

l

are known? (a)

\dfrac{n}{2}\,(2a + l)

(b)

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

(c)

n(a + l)

(d)

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