## 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. Given: $2,4,8, 16,32,.....$ $d=4-2=2 \\ 8-4 =4 \\16-8 =8$ We can see that the common difference is not the same for the given sequence. This is the reason we cannot apply the formula $S_n=\dfrac{n}{2}[a_1+a_n]$ to find the sum of the terms. Thus, the given statement does not make sense.