Question

[An Nguyễn Bá]

Tính tổng: S= \(\left(-\frac{1}{7}\right)^0+\left(-\frac{1}{7}\right)^1+\left(-\frac{1}{7}\right)^2+...+\left(-\frac{1}{7}\right)^{2007}\)

Answer 1

[Ngọc Thái]

S=1+(-1/7)^1+(-1/7)^2+...+(-1/7)^2007

=>7S=7+(-1/7)^1+(1/7)^2+...+(-1/7)^2006

=>(7-1)S=6-(1/7)^2007

=>S=1-(-1/7^2007/6)

Answer 2

[Nguyễn Thị Hồng Nhung]

1/7S=(-1/7)^1+...+(-1/7)2018

1/7S-S=(-1/7)^1+....+(-1/7)^2018-(-1/7)^0-...-(-1/7)^2017

-6/7S=(-1/7)^2018-1=(-1/7)^2018-1:-6/7