Question

Write the sum using summation notation, assuming the suggested pattern continues.

-4 + 5 + 14 + 23 + ... + 131

Answer 1

Hello,
First , number of numbers: (131-(-4))/9 +1=15+1=16
 [(last number- first number)/ (2th number- 1th number) +1

$\sum_{i=1}^{16}{(-13+i*9) =-13 \sum_{i=1}^{16}{1} + 9*\sum_{i=1}^{16}{i}$

$=-13*16+9*\frac{16*(1+16}{2}=-208+9*136=1016$