Question

Tính nhanh A= 1/5+ 1/15 + 1/45+ 1/135 + 1/405

Answer 1

ta có : 1/5+1/15=1-1/15=14/15

vậy 1/5+1/15+1/45+1/135+1/405=1-1/405=404/405

404/405 NHỚ **** ĐÓ

Answer 2

\(\frac{121}{405}\)

Answer 3

ta có :1/5 + 1/15 = 1- 1/15 =14/15 

vậy :1/5 + 1/15 + 1/45 + 1/135 + 1/405 = 1- 1/405 = 404/405

đáp số : 404/405