Question

Tìm số tự nhiên x,biết:  \(\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+....+\frac{1}{8.9.10}\right).x=\frac{23}{45}\)

Answer 1

\(\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{8.9.10}\right).x=\frac{23}{45}\)

\(\frac{1}{2}.\left(\frac{3-1}{1.2.3}+\frac{4-2}{2.3.4}+...+\frac{10-8}{8.9.10}\right).x=\frac{23}{45}\)

\(\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{8.9}-\frac{1}{9.10}\right).x=\frac{23}{45}:\frac{1}{2}\)

\(\left(\frac{1}{2}-\frac{1}{9.10}\right).x=\frac{46}{45}\)

\(\frac{22}{45}.x=\frac{46}{45}\)

\(x=\frac{46}{45}:\frac{22}{45}\)

\(x=\frac{23}{11}\)

Answer 2

\(\left(\frac{1}{1.2.3}+\frac{1}{2.3.4}+....+\frac{1}{8.9.10}\right).x=\frac{23}{45}\)

Ta có:\(\frac{1}{1.2.3}+\frac{1}{2.3.4}+...+\frac{1}{8.9.10}=\frac{1}{2}\cdot\left(\frac{1}{1.2}-\frac{1}{2.3}+\frac{1}{2.3}-\frac{1}{3.4}+...+\frac{1}{8.9}-\frac{1}{9.10}\right)=\frac{1}{2}\cdot\left(\frac{1}{2}-\frac{1}{9.10}\right)=\frac{1}{2}\cdot\frac{22}{45}=\frac{11}{45}\)

=>\(\frac{11}{45}\cdot x=\frac{23}{45}\)

=>11x=23

=>x=23/11

Answer 3

23/11 bạn nha