Ta có :
\(A=\frac{1}{8.11}+\frac{1}{11.14}+..+\frac{1}{605.608}\)
\(3A=\frac{3}{8.11}+\frac{3}{11.14}+...+\frac{3}{605.608}\)
\(3A=\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{605}-\frac{1}{608}\)
\(3A=\frac{1}{8}-\frac{1}{608}\)
\(A=\frac{75}{608}:3\)
\(A=\frac{25}{608}\)
Ủng hộ mk nha !!! ^_^
Ta có: \(A=\frac{1}{8.11}+\frac{1}{11.14}+.....+\frac{1}{605.608}\)
\(\Rightarrow3A=\frac{3}{8.11}+\frac{3}{11.14}+....+\frac{3}{605.608}\)
\(\Rightarrow3A=\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+....+\frac{1}{605}-\frac{1}{608}\)
\(\Rightarrow3A=\frac{1}{8}-\frac{1}{608}=\frac{75}{608}\)
\(\Rightarrow A=\frac{75}{608}:3=\frac{25}{608}\)
Vậy \(A=\frac{25}{608}\)
Ủng hộ cho mik nha bạn?
Ta có :
A=18.11 +111.14 +..+1605.608
3A=38.11 +311.14 +...+3605.608
3A=18 −111 +111 −114 +...+1605 −1608
3A=18 −1608
A=75608 :3
A=25608
\(A=\frac{1}{8\cdot11}+\frac{1}{11\cdot14}+...+\frac{1}{605\cdot608}\)
\(A\cdot3=\frac{11-8}{8\cdot11}+\frac{14-11}{11\cdot14}+...+\frac{608-605}{605\cdot608}\)
\(A\cdot3=\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+\frac{1}{14}-...+\frac{1}{605}-\frac{1}{608}\)
\(A\cdot3=\frac{1}{8}-\frac{1}{608}\)
\(A\cdot3=\frac{75}{608}\)
\(A=\frac{75}{608}\frac{\cdot}{\cdot}3\)
\(A=\frac{25}{608}\)
