Precalculus (6th Edition) Blitzer

The sum of an arithmetic sequence is given by: $S_n=\dfrac{n}{2}[a_1+a_n]$ and the nth term for an arithmetic sequence is given by $a_n=a_1+(n-1) d$ Here, $a_1 \to$ Initial Term and $d=$ Common difference. In order to compute the first $50$ terms of an arithmetic sequence, we can apply the formula. Thus, the given statement makes sense.