Question

Find the sum of the given arithmetic series.

26 + 19 + 12 + 5 + ... + (–37)

Answer 1

since this is an arithmetic sequence
and here first term is 26 and the common difference is -7
we need to know the number of terms n here

Answer 2

so
-37 = 26 +(n-1)*(-7)
-63 =(n-1)*(-7)
or n-1 =9
n=10

Answer 3

sum of this AP can be found using
sum = (no. of terms) * (first term +last term)/2