Question

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

Answer 1

chia ra từng cái một rồi tính

Answer 2

364/729

Answer 3

Gọi A=1/3+1/9+1/27+1/81+1/243+1/729

3A = \(1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\)

3A-A=\(\left(1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{82}+\frac{1}{243}\right)-\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\right)\)

2A=\(1-\frac{1}{729}=\frac{728}{729}\)

A=728/729 : 2 = 364/729