Question

 

tính nhanh

1/3+1/9+1/27+1/81=1/243=1/729

Answer 1

fuck you

Answer 2

ko hiểu gì hết trơn

Answer 3

\(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+\frac{1}{3^4}+\frac{1}{3^5}+\frac{1}{3^6}\)

\(3A=1+\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+\frac{1}{3^4}+\frac{1}{3^5}\)

=> \(2A=1-\frac{1}{3^6}\)

=> \(A=\frac{1-\frac{1}{3^6}}{2}=\frac{729-1}{729}.\frac{1}{2}=\frac{728}{729.2}=\frac{364}{729}\)