Theo đầu bài ta có:
\(\left(\frac{1}{1\cdot2\cdot3}+\frac{1}{2\cdot3\cdot4}+...+\frac{1}{8\cdot9\cdot10}\right)\cdot x=\frac{23}{45}\)
\(\Rightarrow\frac{\frac{1}{1\cdot2}-\frac{1}{2\cdot3}+\frac{1}{2\cdot3}-\frac{1}{3\cdot4}+...+\frac{1}{8\cdot9}-\frac{1}{9\cdot10}}{2}\cdot x=\frac{23}{45}\)
\(\Rightarrow\left(\frac{1}{1\cdot2}-\frac{1}{9\cdot10}\right)\cdot x=\frac{46}{45}\)
\(\Rightarrow\left(\frac{1}{2}-\frac{1}{90}\right)\cdot x=\frac{46}{45}\)
\(\Rightarrow\frac{22}{45}\cdot x=\frac{46}{45}\)
\(\Rightarrow x=\frac{23}{11}\)
Đặt \(A=\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{8.9.10}\)
\(A=\frac{1}{2}.\left(\frac{2}{1.2.3}+\frac{2}{2.3.4}+...+\frac{2}{8.9.10}\right)\)
\(A=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{8.9}-\frac{1}{9.10}\right)\)
\(A=\frac{1}{2}.\left(\frac{1}{1.2}-\frac{1}{9.10}\right)\)
\(A=\frac{1}{2}.\frac{22}{45}=\frac{11}{45}\)
\(\Rightarrow\frac{11}{45}.x=\frac{23}{45}\)
\(\Rightarrow x=\frac{23}{45}:\frac{11}{45}=\frac{23}{11}\)
Ủng hộ mk nha !!! ^_^
(1/1.2.3 + 1/2.3.4 + ... + 1/8.9.10).x = 23/45
2.(1/1.2.3 + 1/2.3.4 + ... + 1/8.9.10).x = 2.23/45
(2/1.2.3 + 2/2.3.4 + ... + 2/8.9.10).x = 46/45
(1/1.2 - 1/2.3 + 1/2.3 - 1/3.4 + ... + 1/8.9 - 1/9.10).x = 46/45
(1/1.2 - 1/9.10).x = 46/45
(1/2 - 1/90).x = 46/45
(45/90 - 1/90).x = 46/45
22/45.x = 46/45
x = 46/45 : 22/45
x = 46/45 . 45/22
x = 23/11
Vậy x = 23/11
\(\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{8.9.10}\right).x=\frac{23}{45}\)
\(\left(1-\frac{1}{2}-\frac{1}{3}+\frac{1}{2}-\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}-\frac{1}{10}\right).x=\frac{23}{45}\)
\(\left(1-\frac{1}{10}\right).x=\frac{23}{45}\)
\(\frac{9}{10}.x=\frac{23}{45}\)
\(x=\frac{23}{45}:\frac{9}{10}\)
\(x=\frac{46}{81}\)
ủng hộ mk nha !!!! ^_^
