Ta có
B=(-5)^0+(-5)^1+(-5)^2+(-5)^3+........+(-5)^2016+(-5)^2017
⇒5B=(-5)^1+(-5)^2+(-5)^3+(-5)^4+..........+(-5)^2017+(-5)^2018
⇒5B-B=[(-5)^1+(-5)^2+(-5)^3+(-5)^4+..........+(-5)^2017+(-5)^2018]-[(-5)^0+(-5)^1+(-5)^2+(-5)^3+........+(-5)^2016+(-5)^2017]
⇒4B=(-5)^2018-(-5)^0
⇒4B=(-5)^2018-1
⇒B=(-5)^2018-1/4
Vậy B=(-5)^2018-1