Question

What is the sum of the arithmetic sequence 22, 13, 4 ... if there are 28 terms?

3,710
-3,094
-2,786
4,018

Answer 1

so the first term = a = 22
common difference = difference between term and its prev. term = d = 13-22 = -9
no. of terms = n = 28

Sum of AP = S

then,
\[S = \frac n 2 (2a + (n-1)d)\]