Question

An alternate way of representing the sum of $n$ terms of an arithmetic progression is in terms of the first term $a$ and the last term $l$ is?

• A. $S_n=n/2[a-l].$
• B. $S_n=n[a+l].$
• C. $S_n=n/2[2a+l].$
• D. $S_n=n/2[a+l].$

Answer 1

Answer: (D)

$S_n=n/2[a+l].$

The sum of $n$ terms in an arithmetic progression can also be found using just the first and the last term of the progression using the formula $S_n=n/2[a+l]$ where $a$ is the first term and $l$ is the last term. Thus the correct answer is $d$.