Đặt A là kết quả, ta có:
3A = 3 x (1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729)
= 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243
A x 3 - A = 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 - (1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729)
= 1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 - 1/3 - 1/9 - 1/27 - 1/81 - 1/243 - 1/729
= 1 - 1/729
A x 2 = 728/729
A = 364/729
1/3 + 1/9 + 1/27 + 1/81 + 1/24 + 1/729
F=1+1/3+1/9+1/27+...+1/243+1/729
1 + 1/3 + 1/9 + 1/27 + 1/81 + 1/243 + 1/729
tính nhanh:1+1/3+1/9+1/27+1/81+1/243+1/729
Khong qui dong mau hay so sang
A=2015^2013+1/2015^2014+1 va B=2015^2014+1/2015^2015+1
A = ( \(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\) ) \(\frac{729}{364}+100:\subset5X\left(3-1\right)\)
tìm quy luật của dãy số sau
1/3+2/9+1/27+2/81+1/243+2/729+.........
\(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\)
Tính nhanh na
\(1+\frac{1}{1+2}+\frac{1}{1+2+3}+\frac{1}{1+2+3+...+50}\)
\(1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+...+\frac{1}{729}\)
