\(3F=\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{9}+...+\frac{1}{10}-\frac{1}{33}\)
\(3F=\frac{1}{3}-\frac{1}{33}=\frac{30}{99}\)
\(F=\frac{10}{99}\)
F=1/18+1/54+1/108+...+1/990 F=1/3.6 + 1/6.9 + 1/9.12 +...+ 1/30.33 suy ra : 3F= 3/3.6 + 3/6.9 + 3/9.12 +...+3/30.33 3F= 3/3 - 3/6 + 3/6 - 3/9 + 3/9 - 3/12 +...+3/30 - 3/33 3F=1 - 3/33 = 33/33 - 3/33 = 30/33 F= 30/33 : 3 = 30/33 . 1/3
F =10/99
F=1/3.6+1/6.9+...+1/30.33
F=1/3 . ( 3/3.6+3/6.9+...+3/30.33 )
F=1/3 . (1/3 - 1/6 + 1/6 -1/9 +... + 1/30 -1/33)
F =1/3 . (1/3-1/33)
F=1/3.10/33
F=10/99
Vậy F =10/99
\(3F=\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{9}+...+\frac{1}{10}-\frac{1}{33}\)
\(3F=\frac{1}{3}-\frac{1}{33}=\frac{30}{99}\)
\(3F=\frac{1}{3}-\frac{1}{33}=\frac{30}{99}\)
\(F=\frac{1}{18}+\frac{1}{54}+\frac{1}{108}+...+\frac{1}{990}\)
\(\Rightarrow F=\frac{1}{3.6}+\frac{1}{6.9}+\frac{1}{9.12}+...+\frac{1}{30.33}\)
\(\Rightarrow3F=3\left(\frac{1}{3.6}+\frac{1}{6.9}+\frac{1}{9.12}+...+\frac{1}{30.33}\right)\)
\(\Rightarrow3F=\frac{3}{3.6}+\frac{3}{6.9}+\frac{3}{9.12}+...+\frac{3}{30.33}\)
\(\Rightarrow3F=\frac{1}{3}-\frac{1}{6}+\frac{1}{6}-\frac{1}{9}+\frac{1}{9}-\frac{1}{12}+...+\frac{1}{30}-\frac{1}{33}\)
\(\Rightarrow3F=\frac{1}{3}-\frac{1}{33}=\frac{11}{33}-\frac{1}{33}=\frac{10}{33}\)
\(\Rightarrow F=\frac{10}{33}:3=\frac{10}{33}.\frac{1}{3}=\frac{10}{99}\)
có gì ko hiểu thì hỏi tui nha