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*(16*(1+16)/(2)=-208+9*136=1016`