Question

Find the sum of the first 100 terms of the sequence below:

-19, -15, -11, -7, -3, ...
S100

Answer 1

17900

Explanation:

First term a = -19

common difference d = -15-(-19) = 4

number of terms, n = 100

sum of first 100 terms,

n/2(2a+(n-1)d)

= 100/2(2×(-19)+(100-1)4)

= 50×(-38+99×4)

= 50×358

= 17900