Question

D= \(\dfrac{1}{7}+\dfrac{1}{7^2}+\dfrac{1}{7^3}+...+\dfrac{1}{7^{100}}\)

            giúp mình nha !!!! thanks trước

Answer 1

2D=1+1/7+1/7²+...+1/7⁹⁹

2D-D=(1+1/7+1/7²+...+1/7⁹⁹)-(1/7+1/7²+...1/7¹⁰⁰)

D=1-1/7¹⁰⁰

Answer 2

Giải:

D=1/7+1/7²+1/7³+...+1/7¹⁰⁰

7D=1+1/7+1/7²+...+1/7⁹⁹

7D-D=(1+1/7+1/7²+...+1/7⁹⁹)-(1/7+1/7²+1/7³+...+1/7¹⁰⁰)

6D=1-1/7¹⁰⁰

D=1-1/7¹⁰⁰/6

Chúc bạn học tốt!