\(\text{Đ}\text{ặt}:A=1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\)
\(\Rightarrow3A=3+1+\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}\)
\(\Rightarrow3A-A=3-\frac{1}{729}\)
\(\Rightarrow2A=\frac{2186}{729}\)
\(\Rightarrow A=\frac{2186}{729}:2=\frac{1093}{729}\)
tính nhanh:1+1/3+1/9+1/27+1/81+1/243+1/729
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
A = ( \(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}+\frac{1}{243}+\frac{1}{729}\) ) \(\frac{729}{364}+100:\subset5X\left(3-1\right)\)
F=1+1/3+1/9+1/27+...+1/243+1/729
1/3 + 1/9 + 1/27 + 1/81 + 1/24 + 1/729
Tính
a) \(\frac{2}{3}+\frac{2}{9}+\frac{2}{27}+\frac{2}{81}+\frac{2}{243}+\frac{2}{729}\)
b) \(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{37.38.39}\)
1/3+1/9+1/27+1/81+1/243
Tính hơp lý : A = 1/3+1/9+1/27+1/81+1/243
