Question

Answer 1

Tính tổng

Answer 2

\(B=7+7^2+7^3+...+7^{60}\)

\(\Rightarrow7B=7^2+7^3+...+7^{61}\)

\(\Rightarrow6B=7B-B=7^2+7^3+...+7^{61}-7-7^2-7^3-...-7^{60}=7^{61}-7\)

\(\Rightarrow B=\dfrac{7^{61}-7}{6}\)

Answer 3

\(B=7+7^2+7^3+...+7^{60}\)

\(7B=7^2+7^3+...+7^{60}+7^{61}\)

\(7B-B=\left(7^2+7^3+...+7^{61}\right)-\left(7+7^2+7^3+...+7^{60}\right)\)

\(6B=7^{61}-7\Rightarrow B=\dfrac{7^{61}-7}{6}\)

 

 

Answer 4

#heli

B=7+7^2+7^3+......+7^59+7^60

7B=7^2+.....+7^61

lấy 7B-B

7B-B=7^2+.....+7^61-(7+7^2+7^3+......+7^59+7^60)

6B=7^61-7

=>B=(7^61-7)/6